REST API

A quick post to explain what a REST API is and how it can be used. I’m clearly making no assumptions about what you know and this is a very brief explanation of a can be very complex topic.

A REST API defines a set of functions which developers can perform requests and receive responses via HTTP protocol such as GET and POST.
Because REST API’s use HTTP, they can be used by practically any programming language and easy to test (it’s a requirement of a REST API that the client and server are independent of each other allowing either to be coded in any language and improved upon supporting longevity and evolution).

The World Wide Web (WWW) is an example of a distributed system that uses REST protocol architecture to provide a hypermedia-driven interface for websites. I’m saying hypermedia (instead of hypertext) as an expansion term to avoid confusion about the REST API supporting other formats to be provided not just HTML.

A Real World Example 

Twitter provides a REST API which you can query to get the latest tweets, you can provide a search query (or hash tag) and it will return the results in JSON format. Example of this HTTP request to the Twitter API to get the latest 3 tweets matching “jQuery”. Try it.

http://search.twitter.com/search.json?q=jQuery&result_type=recent&rpp=3

And to expand on what a REST API should provide:

The REST API should specify what it can provide and how to use it, details such as query parameters, response format, request limitations, public use/API keys, method (GET/POST/PUT/DELETE), language support, callback usage, HTTPS support and resource representations should be self-descriptive…
This is the information provided for the GET search/tweets REST API.


What is REST?

REST stands for Representational state transfer which essentially refers to a style of web architecture that has many underlying characteristics and governs the behavior of clients and servers.

What can use a REST API?

REST API lets you interact with Parse from anything that can send an HTTP request. See Parse REST Definition for examples of this.

REST API’s in the Real World

Welcome the big boys.

The Twitter REST API
Facebook REST API (deprecating)
Google Translate REST API
Flickr REST API
Dropbox REST API
Ebay Developer REST API (product centers)
BING Maps REST API (services)
BING Traffic Incidents API
Magento REST API

What is meant by the term “RESTful API”?

Conforming to the REST constraints is generally referred to as being “RESTful”
An API can be considered “RESTful” if it has the following features (not a complete list just the main ones):

Client–server – The client handles the front end the server handles the backend and can both be replaced independently of each other.

Stateless – No client data is stored on the server between requests and session state is stored on the client.

Cacheable – Clients can cache response (just like browsers caching static elements of a web page) to improve performance.

Complying with these constraints, and thus conforming to the REST architectural style enables any kind of distributed hypermedia system to have desirable emergent properties, such as performance, scalability, simplicity, modifiability, visibility, portability, and reliability. A common trend I have seen is to use absolute urls for RESTful APIs which are meaningful.

Example Dropbox API for file operations


The “RESTful” Client Server Architecture

HTTP, for example, has a very rich vocabulary in terms of verbs (or “methods”), URIs, Internet media types, request and response codes, etc. REST uses these existing features of the HTTP protocol, and thus allows existing layered proxy and gateway components to perform additional functions on the network such as HTTP caching and security enforcement.

RESTful Web Services (API)

A RESTful web service (also called a RESTful web API) is a web service implemented using HTTP and the principles of REST. It is a collection of resources, with four defined aspects:
the base URI for the web service, such as http://example.com/resources/

the Internet media type of the data supported by the web service. This is often XML but can be any other valid Internet media type provided that it is a valid hypertext standard.
the set of operations supported by the web service using HTTP methods (e.g., GET, PUT, POST, or DELETE).

It is a collection of resources, with four defined aspects:

The base URI for the web service, such as http://example.com/resources/

the Internet media type of the data supported by the web service. This is often JSON, XML or YAML but can be any other valid Internet media type.
the set of operations supported by the web service using HTTP methods (e.g., POST, GET, PUT or DELETE).

The API must be hypertext driven.[11]

Popular REST API Request Formats
REST
XML-RPC
SOAP

Also see: The Main Differences Between SOAP and REST APIs

Popular REST API Response Formats

I work mostly with JSON it seems to be the most popular for jQuery developers, for obvious reasons.

REST
XML-RPC
SOAP
JSON
PHP

Do I need an API key to access a REST API?

Most API’s have a request limit and might ask you to provide an API key (which you may have created an application with them). Data sensitive APIs will require you to authenticate and the most popular method is Open Authentication also known as oAuth. I’ve touched briefly on this before on How Twitter oAuth works. Won’t go into oAuth here.

Example is Google Translate requires your API Key in a GET request.

https://www.googleapis.com/language/translate/v2?key=INSERT-YOUR-KEY&source=en&target=de&q=Hello%20world

So is it a REST API or just an API?

Well to decide this you will have to stufy the documentation and determine if the API satisfies the criterion to qualify it to be RESTful. The Atom API is a good example of one that truely qualifies it to be RESTful.

Redhat 6 and 7 Comparison features list

ON THE BASIS OF RELEASE DATE.


RELEASE DATE OF RHEL6 IS 10th NOV 2010.

RELEASE DATE OF RHEL7 IS 10TH JUNE 2014.

Hence RHEL7 is latest os.


DIFFERENCE ON THE BASIS OF OPERATING SYSTEM NAMES


If you want to see this use this command

#cat /etc/redhat-release

RHEL6 : REDHAT ENTERPRISE LINUX (SANTIGO)

RHEL7: REDHAT ENTERPRISE LINUX (MAIPO)



KERNEL VERSION


RHEL6: 2.6.32

RHEL7:  3.0.10


OS BOOT TIME


RHEL6: 40 sec

RHEL7: 20 sec


MAXIMUM SIZE OF SINGLE PARTITION


RHEL6: 50TB(EXT4)

RHEL7: 500TB(XFS)


BOOT LOADER


RHEL6:  /boot/grub/grub.conf

RHEL7: /boot/grupb2/grub.cfg


PROCESSOR ARCHITECTURE


RHEL6: It support 32bit & 64bit  both

RHEL7: It only support 64bit


HOW TO FORMAT OR ASSIGN A FILE SYSTEM IN


RHEL6:      #mkfs.ext4   /dev/hda6

RHEL7:       #mkfs.xfs   /dev/hda6


HOW TO REPAIR A FILE SYSTEM IN


RHEL6:  #fsck -y /dev/hda6

RHEL7:  #xfs_repair /dev/hda6



COMMAND TO MANAGE NETWORK IN RHEL6 AND RHEL7


RHEL6:  #setup

RHEL7:  #nmtui



HOSTNAME CONFIGURATION FILE


RHEL6:    /etc/sysconfig/network

RHEL7:    /etc/hostname


DEFAULT ISO IMAGE MOUNT PATH


RHEL6: /media

RHEL7: /run/media/root



FILE SYSTEM CHECK


RHEL6:   e2fsck

RHEL7:   xfs_repair



RESIZE A FILE SYSTEM


RHEL6:   #resize2fs  -p /dev/vg00/lv1

RHEL7:    #xfs_growfs  /dev/vg00/lv1


TUNE A FILE SYSTEM


RHEL6: tune2fs

RHEL7: xfs_admin



IPTABLES AND FIREWALL


RHEL6: iptables

RHEL7: firewalld



NOTE:


To see firewall status in RHEL7

#firewall-cmd   –state


To see Firewall status in RHEL6

#service iptables status


To stop firewall in RHEL7

#systemctl stop firewalld.service


To stop firewall in RHEL6

#service iptables stop




COMMUNICATION BETWEEN TCP AND UDP IN BACK END


RHEL6: netcat

RHEL7: ncat


INTERFACE NAME


RHEL6: eth0

RHEL7: ens198(N)



COMBINING NIC


RHEL6: Network Bonding

RHEL7: Team Driver



NSF Server Version


RHEL6:  NFSv2

RHEL7:  NFSV4


DATABASE USED


RHEL6: Mysql

RHEL7: mariaDB

Altough RHEL7 also support Mysql



MANAGING SERVICES


RHEL6:

#service sshd restart#chkconfig sshd on

RHEL7:

#systemctl restart sshd#systemctl enable shhd



ON Basis of file System.


RHEL6 defualt file system is ext4 while xfs is RHEL7 default file system.


Kernel Version


RHEL6 default kernel version is 2.6 while RHEL7 is 3.10


Kernel Code Name


RHEL6 kernel code name is Santiago while RHEL7 kernel code name is Maipo.


UID Allocation


In RHEL6 default UID assigned to users would start from 500 while in RHEL7 its starting from 1000.
But this can be changed if required by editing /etc/login.defs file.

Maximum supported File Size.


In RHEL6 maximum file size of an individual file can be up to 16TB while in RHEL7 it can be up to 500TB which is very large in comparison to RHEL6.


Maximum Supported File System Size.


In RHEL6 maximum file system size=16TB(for 64bit Machine) and 8TB(for 32 bit machine). While in RHEL7 maximum file system size is 500TB.

Also keep in mind thatRHEL does not support XFS on 32-bit machines.

change in file system structure.

in rhel6 /bin,/sbin,/lib and /lib64 are usually under / while in rhel7 now they are nested under /usr.



NEW FEATURES OF RHEL7 :



1. Space Required to Install RHEL7
Now if you want to install RHEL7 in your machine, RedHat recommends minimum 5 GB of disk space to install this release of RHEL series for all supported architectures.

2. Boot Loader in RHEL7
A new book loader GRUB2 has been introduced in RHEL 7.It comes with new features.


3.RHEL7 GRUB2 Configuration File:
# vim /boot/grub2/grub.cfg


4. New Installer you can say Redesigned Anaconda Version
Red Hat Enterprise Linux 7 has and redesigned Anaconda version.
It contains many improvements in system installation.


5. firstboot Implementation
RHRL 7 replaces firstboot with the Initial Setup utility, initial-setup, for better interoperability with the new installer.


6. Changes in File System Layout
RHEL7 introduces two major changes to the layout of the file system.
The /bin, /sbin, /lib and /lib64 directories are now under the /usr directory.
The /tmp directory can now be used as a temporary file storage system (tmpfs)



7. Network Configuration utility(ncat)
A new networking utility ncat has been introduced in RHEL 7 which replaces netcat.
8. New Version of Apache
RHEL 7 is coming with apache 2.4



9. Chrony – A new Package Introduced
Chrony is introduced as new NTP client provided in the chrony package. Chrony does not provides all features available in old ntp client (ntp). So ntp is still provided due to compatibility.


10. HAProxy
HAProxy has been introduced in RHEL 7. It is a TCP/HTTP reverse proxy that is well-suited to high availability environments.



11.hostname lookup and setup

In rhel5 and rhel6 version of Linux we need to edit file /etc/sysconfig/network to set hostname but in rhel7 its not so.

Now in RHEL7 we can directly chnage the hostname using below commands.

hostnamectlnmtuinmcli


HOW TO SEE HOSTNAME IN RHEL6 and RHEL7


in RHEL6              #hostname

in RHEL7              #hostnamectl  status   and #hostname


12.Introduction of Docker in RHEL7.

13.Device Hotplug Removed from RHEL7.

14.RHEL7 does not provide 32 bit iso.RHEL7 will not natively support

32-bit hardware architecture.


15.RHEL7 use OPenJDK7 as the default java development kit.


There are other so many changes between RHEL previous versions and RHEL7.

Netstat and ifconfig commands also disappeared from RHEL7 but it can be used by installing net-tools.

The move from sysvinit to systemd is one of most important change that has been made and which is a matter of concerned.

command tail -n is replaced by journalctl -n

command tail -f is replaced by journalctl -f

for displaying kernel messages instead of dmesg now in RHEL7  we use journalctl -k

About Raw Device Mapping

RDM is a mapping file in a separate VMFS volume that acts as a proxy for a raw physical device, a SCSI device used directly by a virtual machine. The RDM contains metadata for managing and redirecting disk access to the physical device.

The file gives you some of the advantages of direct access to a physical device while keeping some advantages of a virtual disk in VMFS. As a result, it merges VMFS manageability with raw device access.

RDMs can be described in terms such as mapping a raw device into a datastore, mapping a system LUN, or mapping a disk file to a physical disk volume. All these terms refer to RDMs.

Raw Device Mapping

Although VMware recommends that you use VMFS datastores for most virtual disk storage, on certain occasions, you might need to use raw LUNs or logical disks located in a SAN.

For example, you need to use raw LUNs with RDMs in the following situations:

■	When SAN snapshot or other layered applications are run in the virtual machine.  The RDM better enables scalable backup offloading systems by using features inherent to the SAN.
■	In any MSCS clustering scenario that spans physical hosts —  virtual-to-virtual clusters as well as physical-to-virtual clusters.  In this case, cluster data and quorum disks should be configured as RDMs rather than as files  on a shared VMFS.

Think of an RDM as a symbolic link from a VMFS volume to a raw LUN. The mapping makes LUNs appear as files in a VMFS volume. The RDM, not the raw LUN, is referenced in the virtual machine configuration. The RDM contains a reference to the raw LUN.

Using RDMs, you can:

■	Use vMotion to migrate virtual machines using raw LUNs.
■	Add raw LUNs to virtual machines using the vSphere Client.
■	Use file system features such as distributed file locking, permissions, and naming.

Two compatibility modes are available for RDMs:

■	Virtual compatibility mode allows an RDM to act exactly like a virtual disk file, including the use  of snapshots.
■	Physical compatibility mode allows direct access of the SCSI device for those applications  that need lower level control.

Defuse an Angry Customer

Use these six steps to cut through the drama so you can address your customer's actual problem

If you work with customers long enough, you'll eventually encounter one who's furious about something or other and can't resist yelling or otherwise acting abusive.

Your challenge is to address the problem with minimum wear and tear--for you, your staff, and the customer. Here's how.

1. Don't take it personally.

Regardless of what customers may believe, the real reason they're is yelling at you is always about something else that's going on in their lives.  It's just your bad luck that you're in the line of fire when the customer is having a horrible day, week, or year.

2. Do not react to the anger.

When confronted by anger, most people react one of two ways: 1) becoming angry themselves or 2) attempting to placate to make peace. Both approaches are mistakes in this case. If you become angry, it only feeds the customer's anger. And if you placate, you'll simply be training the customer to continue to act like a jackass.

3. Expect and demand civility.

State clearly and firmly that you're willing to help resolve the problem, but you won't be yelled at or treated disrespectfully. Don't mince words. Make it clear that your help is dependent upon the customer's ability to behave in a civilized manner. In most cases, the customer will actually breathe a sigh of relief.

4. If the customer won't comply, end the conversation.

Do this politely but firmly. State that you'll be glad to help once the customer is willing to treat you with the respect that you deserve.

Yes, you may lose that customer. However, you've also lost the constant headache that customer will become if you don't set reasonable boundaries.

5. Apologize for the problem.

After you've demanded and received civil behavior--and only then--apologize for the inconvenience that the problem has caused the customer. Then explain that you are just as committed as the customer to resolving the problem fairly and equitably.

6. Work on the problem.

Now that you've established rapport and the fact that you won't be abused, you can go ahead and work on the customer's issue. If the problem can't be resolved immediately, set up a way to report your progress.

You need to follow up religiously, because that will prove you're worthy of keeping the customer's business.

How to enable logging to troubleshoot NetBackup

Basic troubleshooting for Veritas Netbackup

Below are some basic areas which any newbie use to diagnose the problem.

1.) Space

Check the space in the Disk Storage Units, Tapes, Disk arrays etc


2.) Network Connectivity

Check the physical network connectivity via ping command


3.) Services

Verify that the Netbackup Services is being run at Netbackup Server from:

Netbackup Administration Console-->Activity Monitor-->Services

Verify that the Netbackup Client Service is started at client from:

Start-->Settings-->Control Panel-->Administrative Tools-->Services


4.) Check the Name Resolution


On the Master Server:


• …Program Files\Veritas\NetBackup\bin>bpclntcmd.exe -hn Client name

On the client:

• ….Program Files\Veritas\NetBackup\bin>bpclntcmd.exe –pn

• ….Program Files\Veritas\NetBackup\bin>bpclntcmd -ip <clients ip address>


5.) Create Log folders

After creating the below log folders the logs start creating which we can help us to troubleshoot the problem.

• Create on client bpbkar folder under:

<install path>\netbackup\logs

bpbkar is creates a list of files which backups.

• Create bpbrm,bptm,bpcd folders under ….Program Files\Veritas\NetBackup\logs

• Go to Netbackup Administration Console-->Host Properties-->Master Server-->Properties-->Logging-->under Process Specific override--> select 5 from the drop down box for BPBRM,BPCD

• At client side create the folders bpcd and dbclient under
<install path>\netbackup\logs

• Go to Backup, Archive and restore window-->File-->Netbackup Client Properties-->Troubleshooting-->write 5 in the verbose and 9 in the database box

Setting up logs in NetBackup


For a given issue, it may be necessary to gather multiple logs.  This MUST cover the time the issue happens.
If an additional log is required, that has to be created, then ALL the logs must be supplied again.

There are two types of logs in NetBackup.  Legacy logs and VX logs.


1) Creating Legacy Logs
2) Setting Verbose Level for Legacy Logs
3) Collecting Legacy Logs
4) Creating VX Logs and setting the log level
5) Collecting VX logs
6) Volmgr Logs


1) Creating Legacy Logs
************************

These are created in either

Unix
/usr/openv/netbackup/logs/
/usr/openv/volmgr/debug/

Windows
<install path>\veritas\netbackup\logs
<install path>\veritas\volmgr\debug


For example to create bptm log, simply create a directory called the <process> name.

mkdir /usr/openv/netbackup/logs/bptm

A newly created log will not log anything /detect a change of verbose level until the process is restarted.  For logs such as bptm, this will be when the next backup runs.  Other logs such as bprm and bpdm may require a restart of the NBU services.  I say 'may', if the process starts a child process, then this would write to a newly created log or pick up a verbose level change.


2) Setting Verbose Level for Legacy Logs
****************************************

There are two ways this can be done :

(Unix) 

To increase the verbose level of all logs (except vault)
Add the entry VERBOSE = <level> into /usr/openv/netbackup/bp.conf.  <level> is a value between 0 and 5, with 5 being the highest.


(Windows)

On the server you are gathering the logs from, run the BAR GUI
From the File menu, select Client Properties and in the pop-up window, goto the Troubleshooting tab.
Set General to 2 and Verbose to 5


3) Collecting Legacy Logs
*************************

The log file is simply found in the <process> name directory.  There is one log per day.

The name of the log file will be log.<date>

If you are sending multiple log files in, they will all have the same name.  Please therefore rename the log files to :

<process>.log.<date>


4) Creating VX Logs and setting the log level
**********************************************

These are more complex, and have to be set with specific commands.  NOTE: Some of these logs, for example, 'mds' do NOT create a log file.  Instead the lines are entered in to other log files.  In the case of mds (143), it logs into EMM (111).


The vxlogs cover various processes, for example, nbemm, nbrb, nbjm, nbrb, mds


To set these up on either Unix or Windows, use this command :

vxlogcfg -a -p 51216 -o <oid> -s DebugLevel=<1-6> -s DiagnosticLevel=<1-6>

For example, to set the EMM and MDS logs to levels 6 and 6 use

vxlogcfg -a -p 51216 -o 111 -s DebugLevel=6 -s DiagnosticLevel=6
vxlogcfg -a -p 51216 -o 143 -s DebugLevel=6 -s DiagnosticLevel=6


To confirm the log level has been set, simply look in the nblog.conf file, which is located in the netbackup diorectory.

(NOTE: DO NOT EDIT THIS FILE MANUALLY)


5) Collecting VX Logs
*********************

To collect the vx logs, use the nbcplogs command.  This copies the raw logs, which is the preference of Technical Support.

NOTE:  The destination directory MUST be empty.


nbcplogs --no-nbsu -d 2hrs --logs nbemm,nbjm /tmp/logs   (Ex.  Coleect the past 2 hrs of logs, RELATIVE, to when the command is run )
 
nbcplogs --no-nbsu -s 07/11/2012-10:17:58 -e 07/11/2012-12:17:58 --logs nbjm,nbpem /tmp/logs (Collect the logs between two times -s <start> -e <end>  )

In these examples, the nbpem and nbjm logs would be copied to /tmp/logs


For details of using vxlogview please see TN:  http://www.symantec.com/docs/TECH75805


6) Volmgr Debug Logs
********************

These are very similar to legacy logs, the difference being the location and the verbose setting.
There is no value for verbose level, simply it is turned up by adding the work VERBOSE to a line in the vm.conf file.

To turn on Media Manager logging:


UNIX:

Add VERBOSE to the /usr/openv/volmgr/vm.conf file.  If this file does not exist, just create it.
If necessary, create the directory /usr/openv/volmgr/debug

mkdir /usr/openv/volmgr/debug/acssi
mkdir /usr/openv/volmgr/debug/acsd
mkdir /usr/openv/volmgr/debug/robots
mkdir /usr/openv/volmgr/debug/daemon
mkdir /usr/openv/volmgr/debug/ltid
mkdir /usr/openv/volmgr/debug/oprd
mkdir /usr/openv/volmgr/debug/reqlib
mkdir /usr/openv/volmgr/debug/tpcommand

The following empty files increase the details logged further

touch /usr/openv/volmgr/DRIVE_DEBUG
touch /usr/openv/volmgr/ROBOT_DEBUG
touch /usr/openv/volmgr/AVRD_DEBUG
touch /usr/openv/volmgr/SSO_DEBUG


Restart ltid :

/usr/openv/volmgr/bin/stopltid
/usr/openv/volmgr/bin/ltid -v


Windows:

Add VERBOSE to the <install path>\veritas\volmgr\vm.conf file.  If this file does not exist, just create it.

If necessary, create the directory /usr/openv/volmgr/debug

<install path>\veritas\volmgr\debug/acsssi
<install path>\veritas\volmgr\debug/acsd
<install path>\veritas\volmgr\debug/robots
<install path>\veritas\volmgr\debug/daemon
<install path>\veritas\volmgr\debug/ltid
<install path>\veritas\volmgr\debug/oprd
<install path>\veritas\volmgr\reqlib
<install path>\veritas\volmgr\debug\tpcommand

Create the following empty files to increase the details logged further
Ensure that windows does not craete a 'suffix', for example .txt

<install path>\veritas\volmgr\DRIVE_DEBUG
<install path>\veritas\volmgr\ROBOT_DEBUG
<install path>\veritas\volmgr\AVRD_DEBUG
<install path>\veritas\volmgr\SSO_DEBUG


Restart ltid :

<install path>\veritas\volmgr\bin/stopltid
<install path>\veritas\volmgr\bin/ltid -v


NOTE:

The 'OIDs' for the Unified /VX logs can be determined by looking in the nblog.conf file in the /usr/openv/netbackup directory.  Be careful not to edit the file.

The default logs levels for the Unified /VX log levels can be found in the nblog.conf.  These are set as follows:

NetBackup Server : Default.DiagnosticLevel=6 / Default.DebugLevel=1
NetBackup Appliance : Default.DiagnosticLevel=6 / Default.DebugLevel=5



For ORACLE and RMAN  Backup Issue :-

How to enable logging to troubleshoot NetBackup for Oracle RMAN backup and Restore

Solution

The majority of cases at Veritas require the collection of log files in order to determine the nature of the backup or restore problem. Given the comprehensive nature of NetBackup (tm), knowing which logs to collect and which logs are unnecessary can present a daunting task.

This TechNote is designed to assist a user in determining what logs a Support Engineer needs to see in order to expedite the troubleshooting of an Oracle case. While there are cases where logs other than the ones documented are required for resolution, this TechNote should cover the requirements for nearly all cases.

By default, log files are placed in the <install_path>\veritas\netbackup\logs (Windows) and /usr/openv/netbackup/logs (UNIX/Linux) directories on a NetBackup server.


To enable logging on any of the NetBackup processes, a subdirectory must be created in the NetBackup logs directory on the NetBackup host.


Unix: /usr/openv/netbackup/logs

Windows: <install_path>\Veritas\NetBackup\logs


The following log folders should be created on the Oracle client server:

dbclient: 

This log contains debugging information and execution status for the NetBackup Oracle client processes.  Ensure that the Oracle user has permissions to write to this directory.

bpdbsbora: 

This log contains debugging information and execution status for the bpdbsbora utility which saves, retrieves and executes templates.

bphdb: 

This log contains debugging information for the process that executes the backup/restore script or template.  The obk_stdout and obk_stderr logs contain the stdout and stderr from the script if it does not redirect those outputs elsewhere.

bpubsora: 

This log contains debugging information and execution status for Template Wizard connections to the Oracle instance during database browse and template creation.  If logging into the Wizard as the Oracle user, than the directory must be writable by that user.

user_ops: 

This directory is created automatically and must remain readable and writeable by the Oracle user. The comm and progress files therein are updated by the NetBackup server processes as the backup or restore progresses.  It is always present, and should be gathered for most cases.

bpcd:

This log contains debugging information for the connection attempts to update the comm and progress files.

vnetd: 

This log contains debugging information for the connection attempts from the servers to bpcd and dbclient.

Create the following directories on the media server:

bpbrm: 

The bpbrm process handles backup and restore requests.

bptm: 

The bptm process handles interactions with the tape device. If backing up to a disk storage unit, the bpdm folder should be created.  At NetBackup 6.5 and above, bptm is used for both tape and disk storage units.

Create the following directory on the master server:

bprd: 

The bprd process handles the inbound backup, list, and restore requests from the client server.

bpcompatd: 

May be needed in rare instances if nbjm is unable to connect to the client to update comm files.

nbpem and nbjm may be needed occassionally if the jobs do not go Active in a timely manner for the expected policy.

If this is an RMAN PROXY backup with the Snapshot Client, then include these additional logs:

bpfis: 

From both the backup client and the off-host client.

vnetd and bpcd: 

From the off-host client.

To set the debugging level, go into the Backup, Archive and Restore GUI, and select File | NetBackup Client Properties, and click on the Troubleshooting tab. Increase the General, Verbose, and Database levels to 5. On Unix, the debug level can be changed by editing the bp.conf file and adding the following line:

VERBOSE = 5

If the problem is a performance issue, use VERBOSE = 6 to display delays between dbclient and Oracle.  (This applies only to 5.x and 6.5.4 and above).

In order to ensure the processes pick up the new verbosity settings, it is best to stop and restart all the NetBackup services on the hosts.  These processes are key.  The bprd process can pick up a verbosity change via bprdreq -rereadconfig but requires a restart if the logging directory was created.  The bpbrm and bptm processes do not require a restart unless the job will join a long running MPX group.

On Windows, the Oracle processes must be stopped and restarted for dbclient to pickup up a verbosity change.

Once logging is enabled, run the backup or restore, and collect and send the following information for the Support Engineer to review:

1. Collect the logs from the above directories, making sure to rename the files to reflect the folder from which the log comes, and forward to the Support Engineer

2. In addition, on the Oracle client, send the script file (rename it to .txt so it isn't stripped off by anti-virus software), the Recovery Manager (RMAN) output file, the initSID.ora file, and the zipped contents of the user_ops directory.

3. In the bphdb directory, there should be two additional sets of files, oracle_stdout.<date> and oracle_stderr.<date>. Send these files from the date of the backup or restore attempt.

4. Note the names each of the machines

Additionally, it is extremely helpful to have basic system and configuration information from each of the servers involved in the backup or restore.  For NetBackup 6.x and above, run nbsu on the servers.



To check progress on backup jobs you can use :-


bdbjobs -jobid <id> -U


For restores, you have an option to create the log file when you configure the restore. Look into that particular log file to check progress. Alternatively you can use /usr/openv/netbackup/logs/user_ops/<user name who started the job>/logs


The purpose of this post is to provide a single location for info to be able to set up logs.
The details below are just about the shortest version I can make, that still contains detail/ explanation.

Any NetBackup Engineer should be able to set up logs with the minimum of information, all that 'should be required' for example.

"Please set bptm/ bpbrm on windows media xxx at verbose 5/ general 2 and bpdbm on unix master at versbose 5".

PTE Academic Practice Tests Plus with Key - 2013

The complete PTE Academic practice tests plus with answer key can be downloaded from below link.



https://drive.google.com/file/d/0B6xYh8jQdvfMUURFLTVzRzdVSjQ/view?usp=sharing

Checking for errors and detecting packet loss on Brocade 8000 Switch

Purpose :-

Here are some basic commands for checking the health and status of the brocade 8000 network switches in DCA version 1


Commands Available in FOS mode :-

switchportshow -------- >High level port information displayed
portshow        -------- >show port stats and errors
porterrshow -------- >Show detailed error counters
portstatsshow -------- >Show detailed port statistics
portstats64show -------- >show detailed 64 bit counters
errdump        -------- >show event logs
firmwareshow -------- >current switch firmware version
switchstatusshow-------- >High level switch information displayed
sensorshow -------- >Show hardware sensors


Commands available in CEE mode

NOTE: Use command "cmsh" to enter CEE mode

i-sw-1:admin> cmsh
switch#
clear counters all      -------- >reset all switch counters
show ip interface brief -------- >Print interface link status
show running-config     -------- >dumo in memory running config
copy running-config     -------- >startup-configsave the in memory running config to the switches startup-config file

show logging -------- >dump switch event logs

supportsave -u root -p changeme -h 172.28.4.250 -d /tmp/i-sw-2 -l scp-------- >copy support save output to /tmp/i-sw-2 directory on mdw

show interface tengigabitethernet 0/x -------- >show interface settings and stats

How to find port errors and check for packet loss

Below example shows over 31 million packets dropped on port 0/4

show qos rcv-queue interface all
Interface TenGigabitEthernet 0/4
  In-use 1078902 bytes, Total buffer 1081344 bytes
  31977776 packets dropped
How to enable Flow control

One may need to enable flow control in cases where the aggregation switch becomes oversubscribed

ssh admin@i-sw-1

i-sw-1# conf term
i-sw-1(config)# interface tengigabitethernet 0/20
i-sw-1(conf-if-te-0/20)# qos flowcontrol tx on rx on
i-sw-1(conf-if-te-0/20)# exit
i-sw-1(config)# interface tengigabitethernet 0/21
i-sw-1(conf-if-te-0/21)# qos flowcontrol tx on rx on
i-sw-1(conf-if-te-0/21)# exit
... repeat for rest of the ports

New Technologies for Cloud Platform.

What is the OPENSTACK?

OpenStack is a free and open-source software platform for cloud computing, mostly deployed as an infrastructure-as-a-service (IaaS). The software platform consists of interrelated components that control hardware pools of processing, storage, and networking resources throughout a data center.


https://en.wikipedia.org/wiki/LXC





What is Lxc container?

LXC (Linux Containers) is an operating-system-level virtualization environment for running multiple isolated Linux systems (containers) on a single Linux control host. The Linux kernel comprises cgroups for resource isolation (CPU, memory, block I/O, network, etc.) that does not require starting any virtual machines.

https://en.wikipedia.org/wiki/LXC





What is KUBERNETES and how to use it?

Kubernetes is an open source orchestration system for Docker containers. It handles scheduling onto nodes in a compute cluster and actively manages workloads to ensure that their state matches the users declared intentions.


http://kubernetes.io/





What is a docker container?


Package your application into a standardized unit for software development. Docker containers wrap a piece of software in a complete filesystem that contains everything needed to run: code, runtime, system tools, system libraries – anything that can be installed on a server.


https://www.docker.com/what-docker

Academic Collocation List - Pearson - PTE Academic

Collocations

A collocation is a combination of words that are commonly used together; the simplest way of describing collocations is to say that they ‘just sound right’ to native English speakers. Other combinations that may mean the same thing would seem ‘ unnatural’. Collocations include noun phrases like ‘ stiff wind’ and‘weapons of mass destruction’, phrasal verbs such as‘to get together’ and other stock phrases such as‘the rich and famous’

It is important to learn collocations, because they are important for the naturalisation of one’s speech. Besides, they broaden one’s scope for expression.

Here is a list of collocations to help you get started:

Collocations starting with the verb ‘do’

Do me a favour

Do the cooking

Do the housework

Do the shopping

Do the washing up

Do your best

Do your hair


Collocations with the verb ‘have’

Have a good time

Have a bath

Have a drink

Have a haircut

Have a holiday

Have a problem

Have a relationship

Have lunch

Have sympathy


Collocations with the verb ‘break’

Break the law

Break a leg

Break a promise

Break a record

Break someone's heart

Break the ice

Break the news to someone

Break the rules


Collocations with the verb ‘take’

Take a break

Take a chance

Take a look

Take a rest

Take a seat

Take a taxi

Take an exam

Take notes

Take someone's place


Collocations with the verb ‘make’

Make a difference

Make a mess

Make a mistake

Make a noise

Make an effort

Make money

Make progress

Make room

Make trouble


Collocations with the verb ‘catch’

Catch the bus

Catch a ball

Catch a cold

Catch a thief

Catch fire

Catch sight of

Catch someone's attention

Catch someone's eye

Catch the flu


Collocations with the verb ‘pay’

Pay respect

Pay a fine

Pay attention

Pay by credit card

Pay cash

Pay interest

Pay someone a visit

Pay the bill

Pay the price


Collocations with the verb ‘keep’

Keep the change

Keep a promise

Keep a secret

Keep an appointment

Keep calm

Keep in touch

Keep quiet

Keep someone's place



Collocations with the verb ‘save’

Save yourself the trouble

Save electricity

Save energy

Save money

Save someone a seat

Save someone's life

Save something to a disk

Save time


Collocations with the verb ‘go’


Go bald

Go abroad

Go astray

Go bad

Go bankrupt

Go blind

Go crazy

Go fishing

Go mad

Go missing

Go online

Go out of business

Go overseas

Go quiet

Go sailing

Go to war


Collocations with the verb ‘come’

Come under attack

Come close

Come direct

Come early

Come first

Come into view

Come last

Come late

Come on time

Come prepared

Come right back

Come to a decision

Come to an agreement

Come to an end

Come to a standstill

Come to terms with

Come to a total of


Collocations with the verb ‘get’

Get the sack

Get a life

Get a job

Get a shock

Get angry

Get divorced

Get drunk

Get frightened

Get home

Get lost

Get married

Get permission

Get ready

Get started

Get the impression

Get upset

Get wet

Get worried


Collocations related to time


Bang on time

Dead on time

Free time

From dawn till dusk

Great deal of time

Early/late 15th century

Make time for

Next few days

Past few weeks

Right on time

Run out of time

Time goes by

Time passes

Waste time


Collocations related to business English


Annual turnover

Keep in mind

Break off negotiations

Close a deal

Close a meeting

Come to the point

Dismiss an offer

Draw a conclusion

Draw your attention to

Launch a new product

Go bankrupt

Go into partnership

Make a profit/loss



The Complete list can be download from below link.

https://drive.google.com/file/d/0B6xYh8jQdvfMVXZHM3JTRjRsQkE/view?usp=sharing

NEW ZEALAND Skilled Migrant Category

If you have skills, qualifications or experience that New Zealand needs you may be able to apply for a resident visa under the Skilled Migrant Category.

The Skilled Migrant Category is a points system based on factors such as age, work experience, your qualifications, and an offer of skilled employment. You must also be aged 55 or under, and meet English language, health, and character requirements.

How it works

1. Self assessment

Check you meet the requirements and calculate your points

To Review Points:-  https://www.immigration.govt.nz/new-zealand-visas/apply-for-a-visa/about-visa/skilled-migrant-category-resident-visa?_ga=1.45136493.813659573.1479367754

2. Submit an Expression of Interest (EOI)

Note the fees and offices information

Submit an EOI online

3. Receive an Invitation to Apply (ITA)

If you have 160 points or more you'll be selected from the EOI pool and be sent an ITA

4. Submit a resident application

Note the fees and offices information

Submit your resident application within six months on the form we provide you with

5. Receive your visa

If successful, you'll be issued either a resident visa or job search visa

Common mistakes to avoid

Skilled Migrant Category applicants often make these mistakes that result in fewer points being recognised:

Qualifications not recognised

If you’re claiming points for your qualifications they need to either be on the List of Qualifications Exempt from Assessment or have been assessed by NZQA.

Get international qualifications recognised for Immigration | NZQA

Work experience not comparable

If you’re claiming points for work experience it must be in the same field as your qualification and job/job offer. If you don’t have a job or job offer then this experience also needs to be in a comparable labour market, in an occupation on the Long Term Skill Shortage List or for a multinational company.

Bonus point requirements not met

To claim qualification and work experience bonus points you need to meet the strict requirements outlined on the Long Term Skill Shortage List.

Skill shortage list checker | Immigration New Zealand

More information

The content on this page is a summary of what can be found on the Immigration New Zealand website. For comprehensive process and requirements guide visit their website section.

https://www.immigration.govt.nz/new-zealand-visas/apply-for-a-visa/about-visa/skilled-migrant-category-resident-visa?_ga=1.245462221.813659573.1479367754

How Brocade supports leap second handling for NTP

The obvious question raised is what happens during the NTP leap second itself.
Specifically, a positive leap second is inserted between second 23:59:59 of a chosen UTC calendar date (the last day of a month, usually June 30 or December 31) and second 00:00:00 of the following date. This extra second is displayed on UTC clocks as 23:59:60. On clocks that display local time tied to UTC, the leap second may be inserted at the end of some other hour (or half-hour or quarter-hour), depending on the local time zone. When ever there is a leap second the NTP server notifies by setting the NTP leap second bits.

On Brocade devices when ever there is a negative leap second, the clock is set once second backward of the following date as described here. On positive leap second the clock suppress second 23:59:59 of the last day of a chosen month, so that second 23:59:58 of that date would be followed immediately by second 00:00:00 of the following date.

Because the Earth's rotation speed varies in response to climatic and geological events, UTC leap seconds are irregularly spaced and unpredictable. Insertion of each UTC leap second is usually decided about six months in advance by the International Earth Rotation and Reference Systems Service (IERS), when needed to ensure that the difference between the UTC and UT1 readings will never exceed 0.9 second.

Immigration New Zealand accepts OET, PTE, IELTS, FCE, TOFEL for visa purposes

Immigration New Zealand announced on 11 October that it will accept PTE, IELTS, FCE, TOFEL as proof of English proficiency for all visa categories where an English language test result may be required.

The People says: “We applaud Immigration New Zealand for giving Various Test candidates the chance to use their test results for their visa application. We share the common vision of supporting healthcare professionals to successfully contribute within the New Zealand healthcare system”.

The New Zealand Immigration website states that hospitals and practices across New Zealand are looking for doctors, midwives, surgeons and 36 other healthcare occupations. It’s estimated that New Zealand will need 380 extra specialists every year to meet the OECD average by 2021, and up to 25,000 more nurses by 2030.

Christchurch
Auckland
Wellington
Dunedin
Hamilton

For more information about the requirements for Skilled Migrant Category visas, go the Immigration New Zealand media centre website:

https://www.immigration.govt.nz/about-us/media-centre/news-notifications/new-zealand-residence-programme-changes/nzrp-smc

For information about migrating to New Zealand, go to:www.immigration.govt.nz/new-zealand-visas


What if I’ve already applied under the Skilled Migrant Category?


If you’ve already applied, the requirements that were in place on the date you made your application will continue to apply to you. You don’t need to meet the new point threshold and the new requirements for English language evidence do not apply to you.

I think I can meet the new points threshold, but I was planning to use my one year of skilled employment in New Zealand as evidence of meeting the English language requirement, so what do the changes to English language mean for me?
If you are invited to apply, you will need to provide an English test if you do not meet any of the other new requirements. If you apply after 21 November, you can use one of the new tests. Your invitation to apply requires you to apply within four months, so you should make sure you organise your test soon after being invited.

What scores will be required on the new English language tests? Where can I find out more information about the tests?

More information scores required for each test are listed below, along with the websites of each testing providers. Remember that if you lodge your application before 21 November 2016 IELTS is the only test INZ can accept.

How long are the English tests valid for?

English language tests are valid for two years from the date they were sat.


IELTS:-

Test : International English Language Testing System (IELTS)
Website : www.ielts.org
Score required for SMC : 6.5


OET:-

Test : Occupational English Test (OET)
Website : www.occupationalenglishtest.org
Score required for SMC : B

Cambridge English:-

Test : Cambridge English: First (FCE) and FCE for Schools
Website :  www.cambridgeenglish.org/exams/first/
Score required for SMC : 176


PTE :-

Test : Pearson Test of English: Academic (PTE: Academic)
Website :  www.pearsonpte.com
Score required for SMC :  58


TOEFL:-

Test : Test of English as a Foreign Language Internet Based Test (TOEFL iBT)
Website : www.ets.org/toefl/ibt/about
Score required for SMC : 79

SAN Related Interveiw Questions

SAN INTERVIEW QUESTION AND ANSWER


Can you describe SAN in your won word?

A storage area network (SAN) is a high-speed special-purpose network (or subnetwork) that interconnects different kinds of data storage devices with associated data servers on behalf of a larger network of users. Typically, a storage area network is part of the overall network of computing resources for an enterprise. 

A storage area network is usually clustered in close proximity to other computing resources such as IBM Power5 boxes but may also extend to remote locations for backup and archival storage, using wide area network carrier technologies such as ATM or SONET .

A storage area network can use existing communication technology such as IBM’s optical fiber ESCON or it may use the newer Fibre Channel technology. Some SAN system integrators liken it to the common storage bus (flow of data) in a personal computer that is shared by different kinds of storage devices such as a hard disk or a CD-ROM player.

SANs support disk mirroring, backup and restore, archival and retrieval of archived data, data migration from one storage device to another, and the sharing of data among different servers in a network. 
SANs can incorporate subnetworks with network-attached storage (NAS) systems.

So you mention NAS, but What is NAS?

Network-attached storage (NAS) is hard disk storage that is set up with its own network address rather than being attached to the department computer that is serving applications to a network’s workstation users. 

By removing storage access and its management from the department server, both application programming and files can be served faster because they are not competing for the same processor resources. The network-attached storage device is attached to a local area network (typically, an Ethernet network) and assigned an IP address. File requests are mapped by the main

server to the NAS file server.

Network-attached storage consists of hard disk storage, including multi-disk RAID systems, and software for configuring and mapping file locations to the network-attached device. Network-attached storage can be a step toward and included as part of a more sophisticated storage system known as a storage area network (SAN).

NAS software can usually handle a number of network protocols, including Microsoft’s Internetwork Packet Exchange and NetBEUI, Novell’s Netware Internetwork Packet Exchange, and Sun Microsystems’ Network File System. Configuration, including the setting of user access priorities, is usually possible using a Web browser.

What is SMTP and how it works?

SMTP (Simple Mail Transfer Protocol) is a TCP/IP protocol used in sending and receiving e-mail. However, since it islimited in its ability to queue messages at the receiving end, it is usually used with one of two other protocols, POP3 or IMAP, that let the user save messages in a server mailbox and download them periodically from the server. 

In other words, users typically use a program that uses SMTP for sending e-mail and either POP3 or IMAP for receiving e-mail. On Unix-based systems, sendmail is the most widely-used SMTP server for e-mail. 

A commercial package, Sendmail, includes a POP3 server. Microsoft Exchange includes an SMTP server and can also be set up to include POP3 support.

SMTP usually is implemented to operate over Internet port 25.

Do you have any idea about NAT?

Short for Network Address Translation, an Internet standard that enables a local-area network (LAN) to use one set of IP addresses for internal traffic and a second set of addresses for external traffic. A NAT box located where the LAN meets the Internet makes all necessary IP address translations.

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NAT serves three main purposes :- 

Provides a type of firewall by hiding internal IP addresses Enables a company to use more internal IP addresses. Since they’re used internally only, there’s no possibility of conflict with IP addresses used by other companies and organizations.

Allows a company to combine multiple ISDN connections into a single Internet connection.

Explain DHCP and its uses to an environment?

Short for Dynamic Host Configuration Protocol, a protocol for assigning dynamic IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address every time it connects to the network. In some systems, the device’s IP address can even change while it is still connected. DHCP also supports a mix of static and dynamic IP addresses.

Dynamic addressing simplifies network administration because the software keeps track of IP addresses rather than requiring an administrator to manage the task. This means that a new computer can be added to a network without the hassle of manually assigning it a unique IP address. Many ISPs use dynamic IP addressing for dial-up users.

What does SNMP stands for?

Short for Simple Network Management Protocol, a set of protocols for managing complex networks. SNMP works by sending messages, called Protocol Data Units, to different parts of a network. SNMP-compliant devices, called Agents, store data about themselves in Management Information Bases and return this data to the SNMP requesters.

What do you know about TCPDump?

TCPdump is a common computer network debugging tool that runs under the command line. It allows the user to intercept and display TCP/IP and other packets being transmitted or received over a network to which the computer is attached. Tcpdump works on most Unix-like platforms: Linux, Solaris, BSD, Mac OS X, HP-UX and AIX among others. On Windows, WinDump can be used; it’s a port of tcpdump to Windows.

You must have a root or super user authority to use TCP dumps in UNIX like environment.

What is software RAID Levels do?

Redundant Arrays of Independent Disks (RAID) is formally defined as a method to store data on any type of disk medium.

LDAP - The Light Directory Access Protocol (LDAP) defines a standard method for accessing and updating information in a directory (a database) either locally or remotely in a client-server model.

What are the benefits of fibre channel SANs?

Fibre Channel SANs are the de facto standard for storage networking in the corporate data center because they provide exceptional reliability, scalability, consolidation, and performance. Fibre Channel SANs provide significant advantages over direct-attached storage through improved storage utilization, higher data availability, reduced management costs, and highly scalable capacity and performance.

What environment is most suitable for fibre channel SANs?

Typically, Fibre Channel SANs are most suitable for large data centers running business-critical data, as well as applications that require high-bandwidth performance such as medical imaging, streaming media, and large databases. Fibre Channel SAN solutions can easily scale to meet the most demanding performance and availability requirements.

What customer problems do fibre channel SANs solve?

The increased performance of Fibre Channel enables a highly effective backup and recovery approach, including LAN free and server-free backup models. The result is a faster, more scalable, and more reliable backup and recovery solution. By providing flexible connectivity options and resource sharing, Fibre Channel SANs also greatly reduce the number of physical devices and disparate systems that must be purchased and managed, which can dramatically lower

capital expenditures. 

Heterogeneous SAN management provides a single point of control for all devices on the SAN,

lowering costs and freeing personnel to do other tasks.

How long has fibre channel been around?

Development started in 1988, ANSI standard approval occurred in 1994, and large deployments began in 1998. Fibre Channel is a mature, safe, and widely deployed solution for high-speed (1 GB, 2 GB, 4 GB) communications and is the foundation for the majority of SAN installations throughout the world.

What is the future of fibre channel SANs?

Fibre Channel is a well-established, widely deployed technology with a proven track record and a very large installed base, particularly in high-performance, business-critical data center environments. Fibre Channel SANs continue to grow and will be enhanced for a long time to come. The reduced costs of Fibre Channel components, the availability of SAN kits, and the next generation of Fibre Channel (4 GB) are helping to fuel that growth. In addition, the Fibre Channel roadmap includes plans to double performance every three years.

What are the benefits of 4gb fibre channel?

Benefits include twice the performance with little or no price increase, investment protection with backward compatibility to 2 GB, higher reliability due to fewer SAN components (switch and HBA ports) required, and the ability to replicate, back up, and restore data more quickly. 4 GB Fibre Channel systems are ideally suited for applications that need to quickly transfer large amounts of data such as remote replication across a SAN, streaming video on demand, modeling

and rendering, and large databases. 4 GB technology is shipping today.

How is fibre channel different from ISCSI?

Fibre Channel and iSCSI each have a distinct place in the IT infrastructure as SAN alternatives to DAS. Fibre Channel generally provides high performance and high availability for business-critical applications, usually in the corporate data center. In contrast, iSCSI is generally used to provide SANs for business applications in smaller regional or departmental data centers. 


When should I deploy fibre channel instead of ISCSI?

For environments consisting of high-end servers that require high bandwidth or data center environments with business critical data, Fibre Channel is a better fit than iSCSI. For environments consisting of many midrange or low-end servers, an IP SAN solution often delivers the most appropriate price/performance.

Name some of the SAN topologies ?

Point-to-point, arbitrated loop, and switched fabric topologies.

What’s the need for separate network for storage why LAN cannot be used?

LAN hardware and operating systems are geared to user traffic, and LANs are tuned for a fast user response to messaging requests.

With a SAN, the storage units can be secured separately from the servers and totally apart from the user network enhancing storage access in data blocks (bulk data transfers), advantageous for server-less backups.

What are the advantages of RAID?

“Redundant Array of Inexpensive Disks”

Depending on how we configure the array, we can have the

- data mirrored [RAID 1] (duplicate copies on separate drives)

- striped [RAID 0] (interleaved across several drives), or

- parity protected [RAID 5](extra data written to identify errors).

These can be used in combination to deliver the balance of performance and reliability that the user requires.

Define RAID? Which one you feel is good choice?

RAID (Redundant array of Independent Disks) is a technology to achieve redundancy with faster I/O. There are Many Levels of RAID to meet different needs of the customer which are: R0, R1, R3, R4, R5, R10, R6. Generally customer chooses R5 to achieve better redundancy and speed and it is cost effective.

R0 – Striped set without parity/[Non-Redundant Array].

Provides improved performance and additional storage but no fault tolerance. Any disk failure destroys the array, which becomes more likely with more disks in the array. A single disk failure destroys the entire array because when data is written to a RAID 0 drive, the data is broken into fragments. 
The number of fragments is dictated by the number of disks in the drive. The fragments are written to their respective disks simultaneously on the same sector. This allows smaller sections of the entire chunk of data to be read off the drive in parallel, giving this type of arrangement huge bandwidth.

RAID 0 does not implement error checking so any error is unrecoverable. More disks in the array means higher bandwidth, but greater risk of data loss

R1 – Mirrored set without parity.

Provides fault tolerance from disk errors and failure of all but one of the drives. Increased read performance occurs when using a multi-threaded operating system that supports split seeks, very small performance reduction when writing.

Array continues to operate so long as at least one drive is functioning. Using RAID 1 with a separate controller for each disk is sometimes called duplexing.

R3 – Striped set with dedicated parity/Bit interleaved parity.

This mechanism provides an improved performance and fault tolerance similar to RAID 5, but with a dedicated parity disk rather than rotated parity stripes. The single parity disk is a bottle-neck for writing since every write requires updating the parity data. One minor benefit is the dedicated parity disk allows the parity drive to fail and operation will continue without parity or performance penalty.

R4 – Block level parity.

Identical to RAID 3, but does block-level striping instead of byte-level striping. In this setup, files can be distributed between multiple disks. Each disk operates independently which allows I/O requests to be performed in parallel, though data transfer speeds can suffer due to the type of parity. The error detection is achieved through dedicated parity and is stored in a separate, single disk unit.

R5 – Striped set with distributed parity.

Distributed parity requires all drives but one to be present to operate; drive failure requires replacement, but the array is not destroyed by a single drive failure. Upon drive failure, any subsequent reads can be calculated from the distributed parity such that the drive failure is masked from the end user. The array will have data loss in the event of a second drive failure and is vulnerable until the data that was on the failed drive is rebuilt onto a replacement drive.

R6 – Striped set with dual distributed Parity.

Provides fault tolerance from two drive failures; array continues to operate with up to two failed drives. This makes larger RAID groups more practical, especially for high availability systems. This becomes increasingly important because large-capacity drives lengthen the time needed to recover from the failure of a single drive. 
Single parity RAID levels are vulnerable to data loss until the failed drive is rebuilt: the larger the drive, the longer the rebuild will take. Dual parity gives time to rebuild the array without the data being at risk if one drive, but no more, fails before the rebuild is complete.

What is the difference between RAID 0+1 and RAID 1+0?

RAID 0+1 (Mirrored Stripped)

In this RAID level all the data is saved on stripped volumes which are in turn mirrored, so any disk failure saves the data loss but it makes whole stripe unavailable. The key difference from RAID 1+0 is that RAID 0+1 creates a second striped set to mirror a primary striped set. The array continues to operate with one or more drives failed in the same mirror set, but if drives fail on both sides of the mirror the data on the RAID system is lost. In this RAID level if one disk is failed full

mirror is marked as inactive and data is saved only one stripped volume.

RAID 1+0 (Stripped Mirrored)

In this RAID level all the data is saved on mirrored volumes which are in turn stripped, so any disk failure saves data loss. The key difference from RAID 0+1 is that RAID 1+0 creates a striped set from a series of mirrored drives. In a failed disk situation RAID 1+0 performs better because all the remaining disks continue to be used. The array can sustain multiple drive losses so long as no mirror loses both its drives.

This RAID level is most preferred for high performance and high data protection because rebuilding of RAID 1+0 is less time consuming in comparison to RAID 0+1.

When JBOD’s are used?

“Just a Bunch of Disks”

It is a collection of disks that share a common connection to the server, but don’t include the mirroring, striping, or parity facilities that RAID systems do, but these capabilities are available with host-based software.

Differentiate RAID & JBOD?

RAID: “Redundant Array of Inexpensive Disks” Fault-tolerant grouping of disks that server sees as a single disk volume Combination of parity-checking, mirroring, stripingSelf-contained, manageable unit of storage 

JBOD: “Just a Bunch of Disks”

Drives independently attached to the I/O channel

Scalable, but requires server to manage multiple volumes

Do not provide protection in case of drive failure

What is a HBA?

Host bus adapters (HBAs) are needed to connect the server (host) to the storage.

What are the advantages of SAN?

Massively extended scalability.

Greatly enhanced device connectivity.

Storage consolidation.

LAN-free backup.

Server-less (active-fabric) backup.

Server clustering.

Heterogeneous data sharing.

Disaster recovery – Remote mirroring.

While answering people do NOT portray clearly what they mean & what advantages each of them have, which are cost effective & which are to be used for the client’s requirements.

What is the difference b/w SAN and NAS?

The basic difference between SAN and NAS, SAN is Fabric based and NAS is Ethernet based.

SAN – Storage Area Network

It accesses data on block level and produces space to host in form of disk.

NAS – Network attached Storage

It accesses data on file level and produces space to host in form of shared network folder.

What is a typical storage area network consists of – if we consider it for implementation in a small business setup?

If we consider any small business following are essentials components of SAN:

Fabric Switch.

FC Controllers.

JBOD’s.

Can you briefly explain each of these Storage area components?

Fabric Switch: It’s a device which interconnects multiple network devices .There are switches starting from 16 port to 32ports which connect 16 or 32 machine nodes etc. vendors who manufacture these kind of switches are Brocade, McData.

What is the most critical component in SAN?

Each component has its own criticality with respect to business needs of a company.

How is a SAN managed?

There are many management software’s used for managing SAN’s to name a few:

Santricity.

IBM Tivoli Storage Manager.

CA Unicenter.

Veritas Volumemanger.

Which one is the Default ID for SCSI HBA?

Generally the default ID for SCSI HBA is 7.

SCSI- Small Computer System Interface.

HBA – Host Bus Adaptor.

What is the highest and lowest priority of SCSI?

There are 16 different ID’s which can be assigned to SCSI device 7, 6, 5, 4, 3, 2, 1, 0, 15, 14, 13, 12, 11, 10, 9, 8.

Highest priority of SCSI is ID 7 and lowest ID is 8.

How do you install device drivers for the HBA first time during OS installation?

In some scenarios you are supposed to install Operating System on the drives connected thru SCSI HBA or SCSI RAID Controllers, but most of the OS will not be updated with drivers for those controllers, that time you need to supply drivers externally, if you are installing windows, you need to press F6 during the installation of OS and provide the driver disk or CD which came along with HBA.

If you are installing Linux you need to type “linux dd” for installing any driver.

What is Array?

Array is a group of Independent physical disks to configure any Volumes or RAID volumes.

Can you describe at-least 3 troubleshooting scenarios which you have come across in detail?

SCENARIO 1: How do you find/debug when there is error while

working SCSI devices?

In our daily SAN troubleshooting there are many management and configuration tools we use them to see when there is a failure with target device or initiator device.

Some time it is even hard to troubleshoot some of the things such as media errors in the drives, or some of the drives taking long time to spin-up. In such cases these utilities will not come to help. To debug this kind of information most of the controller will be implemented with 3-pin serial debug port. With serial port debug connector cable you can collect the debug information with hyper terminal software.

SCENARIO 2: 

I am having an issue with a controller its taking lot of time to boot and detect all the drives connected how can I solve this.?

There are many possibilities that might cause this problem. One of the reason might be you are using bad drives that cannot be repaired. In those cases you replace the disks with working ones.

Another reason might be slots you connected your controller to a slot which might not be supported.

Try to connect with other types of slots. One more probable reason is if you have flashed the firmware for different OEM’s on the same hardware.

To get rid of this the flash utilities will be having option to erase all the previous and EEPROM and boot block entry option. Use that option to rectify the problem.

SCENARIO 3: 

I am using tape drive series 700X, even the vendor information on the Tape drive says 700X, but the

POST information while booting the server is showing as 500X what could be the problem?

First you should make sure your hardware is of which series, you can find out this in the product website.

Generally you can see this because in most of the testing companies they use same hardware to test different series of same hardware type. What they do is they flash the different series firmware. You can always flash back to exact hardware type.

Which are the 4 types of SAN architecture types ?

Core-edge.

Full-Mesh.

Partial-Mesh.

Cascade.

Which command is used in linux to know the driver version of any hardware device?

dmesg.

How many minimum drives are required to create R5 (RAID 5)?

You need to have at least 3 disk drives to create R5.

Can you name some of the states of RAID array?

There are states of RAID arrays that represent the status of the RAID arrays which are given below:

Online.

Degraded.

Rebuilding.

Failed.

What are the protocols used in physical/datalink and network layer of SAN?

Ethernet.

SCSI.

Fibre Channel.

What is storage virtualization?

Storage virtualization is amalgamation of multiple n/w storage devices into single storage unit.

Describe in brief the composition of FC Frame?

Start of the Frame locator

Frame header (includes destination id and source id, 24 bytes/6 words).

Data Payload (encapsulate SCSI instruction can be 0-2112 bytes in length).

CRC (error checking, 4 bytes).

End of Frame (1 byte).

What is virtualization?

Virtualization is logical representation of physical devices. It is the technique of managing and presenting storage devices and resources functionally, regardless of their physical layout or location. Virtualization is the pooling of physical storage from multiple network storage devices into what appears to be a single storage device that is managed from a central console. Storage virtualization is commonly used in a storage area network (SAN). The management of storage devices can be tedious and time-consuming. Storage virtualization helps the storage administrator perform the tasks of

backup, archiving, and recovery more easily, and in less time, by disguising the actual complexity of the SAN.

What is HA?

HA High Availability is a technology to achieve failover with very less latency. Its a practical requirement of data centers these days when customers expect the servers to be running 24 hours on all 7 days around the whole 365 days a year – usually referred as 24x7x365. So to achieve this, a redundant infrastructure is created to make sure if one database server or if one app server fails there is a replica Database or Appserver ready to take-over the operations. End customer never experiences any outage when there is a HA network infrastructure.

Can you name some of the available tape media types?

There are many types of tape media available to back up the data, some of them are:

DLT: Digital Linear Tape – technology for tape backup/archive of networks and servers; 
DLT technology addresses midrange to high-end tape backup requirements.

LTO: Linear Tape Open; a new standard tape format developed by HP, IBM, and Seagate.

AIT: Advanced Intelligent Tape; a helical scan technology developed by Sony for tape backup/archive of networks and servers, specifically addressing midrange to high-end backup requirements.

Can we assign a hot spare to R0 (RAID 0) array?

No, since R0 is not redundant array, failure of any disks results in failure of the entire array so we cannot rebuild the hot spare for the R0 array.

Name the features of SCSI-3 standard?

QAS: Quick arbitration and selection. Domain Validation.

CRC: Cyclic redundancy check.

What is Multipath I/O?

Fault tolerant technique where, there is more than one physical path between the CPU in the computer systems and its main storage devices through the buses, controllers, switches and other bridge devices connecting them.

What is disk array?

Set of high performance storage disks that can store several terabytes of data. Single disk array can support multiple points of connection to the network.

What are different types of protocols used in transportation and session layers of SAN?

Fibre Channel Protocol (FCP).

Internet SCSI (iSCSI).

Fibre Channel IP (FCIP).

What is the type of Encoding used in Fibre Channel?

8b/10b, as the encoding technique is able to detect all most all the bit errors

What are the main constrains of SCSI in storage networking?

Deployment distance (max. of 25 mts).

Number of devices that can be interconnected (16).

What is a Fabric?

Interconnection of Fibre Channel Switches.

What are the services provided by Fabric to all the nodes?

1. Fabric Login.

2. SNS.

3. Fabric Address Notification.

4. Registered state change notification.

5. Broadcast Servers.

What is the difference between LUN and WWN?

LUN: Unique number that is assigned to each storage device or partition of the storage that the storage can support.

WWN: 64bit address that is hard coded into a fibre channel HBA and this is used to identify individual port 

(N_Port or F_Port) in the fabric.

What are the different topologies in Fibre Channel?

1. Point-to-Point.

2. Arbitrary Loop.

3. Switched Fabric Loop.

What are the layers of Fibre Channel Protocol?

1. FC Physical Media.

2. FC Encoder and Decoder.

3. FC Framing and Flow control.

4. FC Common Services.

5. FC Upper Level Protocol Mapping.

What is zoning?

Fabric management service that can be used to create logical subsets of devices within a SAN. This enables portioning of resources for management and access control purpose.

What is the purpose of disk array?

Probability of unavailability of data stored on the disk array due to single point failure is totally eliminated.

How does FC Switch maintain the addresses?

FC Switch uses simple name server (SNS) to maintain the mapping table.

What are the two major classification of zoning?

Two types of zoning are:

1. Software Zoning.

2. Hardware Zoning.

What are different levels of zoning?

1. Port Level zoning.

2. WWN Level zoning.

3. Device Level zoning.

4. Protocol Level zoning.

5. LUN Level zoning.

What are the 3 prominent characteristics of SAS Protocol?

1. Native Command Queuing (NCQ.)

2. Port Multiplier.

3. Port Selector.

What are the 5 states of Arbitrary Loop in FC?

1. Loop Initialization.

2. Loop Monitoring.

3. Loop arbitration.

4. Open Loop.

5. Close Loop.

What is LUN Masking?

A method used to create an exclusive storage area and access control. And this can be achieved by storage device control program.

What is snapshot?

A snapshot of data object contains an image of data at a particular point of time.

What is hot-swapping?

Devices are allowed to be removed and inserted into a system without turning off the system.