About WAN Resiliency

7/16/2019 About WAN Resiliency

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NetBackup Whitepaper

About WAN ResiliencyThis document gives brief introduction about problems faced in WANenvironment and how WAN Resiliency feature addressed in NB 7.5

This document is for internal and external use.

If you have any feedback or questions about this document please

email them to [email protected] stating thedocument title.

This document applies to the following version(s) of NetBackup: 7.5

mailto:[email protected]





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Document Control

Contributors

Who Contribution

Harsha Muktamath

Brijesh Chougule



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Abstract

The purpose of this white paper is to explain how WAN Resiliency can be used in WAN environment. Thispaper explains about the possible network interruptions and how WAN resiliency feature helps to fix theseissues.

Intended Audience

This paper is intended for internal and external audience. It gives an overview of potential WAN issues and

how WAN resiliency feature overcomes it.

Introduction

Every company may have the need to communicate over a WAN environment. A company may need to senddata across a WAN between their Data Centre (in one location) and their remote offices (in other locations). AWAN enables data transfers to happen across geographies with a tradeoff of various network interruptions.These interruptions include (but are not limited to) intermittent disconnections, latency or chit chat, packetlosses, and delays. To overcome these problems, there are multiple solutions available. There are third partytools available which can help an application in recovering from such interruptions but would involve softwarecosts and/or hardware costs. Other solutions might involve making the application itself resilient to suchinterruptions. NetBackup 7.5 includes a feature, Resilient Network, which will help data transfers over a WANenvironment by becoming resilient to WAN interruptions.

Requirements

1) Master server, media servers, and clients should all be running NBU 7.5 or later. Back level media

servers and clients are supported in the environment but for the Resilient Network feature to work, all

machines involved must be running NBU 7.5 or later.

2) The below figure illustrates one scenario where the master server and media servers are in the Data

Centre and the clients are at remote locations.

Note: The figure depicts only some of the supported platforms. Please refer to the Hardware Compatibilityguide for a complete list of supported platforms.



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How it works:

The „Resilient Network‟ feature gives NetBackup 7.5 the ability to recover from network interrupt ions duringoperations between clients in a remote office and the master server and/or media server in the Data Centre.This is accomplished by the following:

1. Enhanced communication between the NetBackup Master/Media Server and the NetBackup Client.Connections between the client and the master server / media server will be resilient to failures. Theconnections will recover from interruptions during communications without causing operations to fail.

2. Enhanced administration and configuration to better suit the needs and requirements of NetBackupClients in a remote office.

Below is a pictorial representation of the supported configuration in a WAN environment. Even though thediagram only lists the Media Server backing up to either BasicDisk or AdvancedDisk, the Media Server canbackup to any type of storage; this includes tape as well as a PureDisk Deduplication-Pool

To set resiliency:

Resiliency can be set using CLI or through GUI.

CLINew resilient_clients command

• Windows: install_path\NetBackup\bin\admincmd

• UNIX: /usr/openv/netbackup/bin/admincmd

resilient_clients status | on | off <nbuclientname>



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GUI

Note: Please refer Symantec NetBackup Deduplication Guide for more information on how to configure theResilient Network feature (using GUI or CLI).

Some information on the WAN network (Good or Bad)

The solution mentioned in the above section works better considering High Availability networks. Thedefinition of a High Availability network is as follows

Availability = MTBF/(MTBF+MTTR).

MTBF – Mean Time Before Failure

MTTR - Mean Time To Repair

24 hours/day * 3600 seconds/hour = 86400 seconds

Availability is 90%; downtime per day is 86400*0.10 = 8640 seconds.

Availability is 99%; downtime per day is 86400*0.01 = 864 seconds.

Availability is 99.9%; downtime per day is 86400*0.001 = 86.4 seconds.




Let us break it down a little more:

When availability is 90%, the downtime per hour is 8640/24 = 360 seconds, and the downtime per 10 minutesis 60 seconds.

When availability is 99%, the downtime per hour is 864/24 = 36 seconds, and the downtime per 10 minutes is6 seconds.

When availability is 99.9%, the downtime per hour is 86.4/24 = 3.6 seconds, and the downtime per 10minutes is 0.6 seconds.

--

As per the industry standards, it has been observed that the networks are available for greater than 99% mostof the times and the worst availability is 97.4%. Anything below this value will constitute for a “Bad Network”;



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in which case no other application (including NetBackup) will work. With the „Resilient Network‟ feature, aNetBackup resilient connection can survive network interruptions of up to 80 seconds and may surviveinterruptions longer than 80 seconds.

A new NBRNTD daemon

In order to protect the connections between a NetBackup client and a NetBackup Media/Master server, a newdaemon, „NBRNTD, is introduced – NetBackup Remote Network Transport Daemon. This daemon maintainsthe connections and will re-establish a broken connection. It is started on demand.

The network resiliency communication includes following aspects:

1. Initiate a protected connection between remote client and data centre(VNETD – NBRNTD<------>NBRNTD-VNETD).

2. Connection reestablishment if the WAN connection is down.3. Data Buffering4. Data Integrity and Consistency

Supportability with external applications:1) Files and folder backup – File system related backup/restore.

2) Virtualization/Flash backups.

3) Database agents backup/restore.

What is not supported?

1) Resilient connections are not supported for

a. Master Server <-> Media Server communications

b. Media Server <-> Media Server communications

2) Optimized duplication is between Storage servers and resiliency between these is not supported.

3) Resilient connections are not supported to the client if the client also happens to be a Master Server

or Media Server.



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Troubleshooting techniques:

With the introduction of new service – NBRNTD, all the connection/reconnection logs are stored under nbrntdlogs.

Connection/Reconnection can be seen in nbrntd logs

9/7/2011 13:15:22.068 [wan_status_notify] [Statistic] 0000000000000204 link_id:8 Network broken! (../local_connection.cpp:1493)

9/7/2011 13:15:22.228 [wan_status_notify] [Statistic] 0000000000000204 link_id:8 Network recovered! (../local_connection.cpp:1487)

Network failures can be identified by SESSION_SWAP messages in pdplugin.log:

09/07/11 14:40:05 [15544] [9532] [DEBUG] PDVFS: pdvfs_lib_log: Sending binary message to <NBU Mediaserver>:10082: SESSION_SWAP 2941385056 4 0: 898404890 0 428019057 27988

09/07/11 14:40:05 [15544] [9532] [DEBUG] PDVFS: pdvfs_lib_log: __crSessionSetupAgain: client has sent428019057 bytes and read 27988 bytes for session id 898404890

09/07/11 14:40:05 [15544] [9532] [DEBUG] PDVFS: pdvfs_lib_log: Received binary message from <NBU

Media server>:10082: SESSION_SWAP 2941385056 4 0: 898404890 0 27988 427887969

09/07/11 14:40:05 [15544] [9532] [DEBUG] PDVFS: pdvfs_lib_log: __crSessionSetupAgain: server sent 0status with 27988 sent bytes and 427887969 read bytes for session id 898404890

Connection/Reconnection messages can also be seen in deduplication engine (spoold) messages:

September 07 15:11:28 WARNING [0000000000C6F3F0]: 25015: resiliency reconnect check, sleeping for 9seconds

September 07 15:11:29 WARNING [0000000000C6F3F0]: 25015: resiliency reconnect check, timeoutcomparing 300 vs 300, attempt no 53

September 07 15:11:29 ERR [0000000000C6F3F0]: 25015: Timed out reached while waiting for session id3235169508 to reconnect. Reconnect Failed.

September 07 15:11:29 ERR [0000000000C6F3F0]: 25036: Could not receive binary message: expected 4bytes got -1 bytes. Cause: connection reset by peer

Recommended Practices:

1) Use Client Side Deduplication: This would help in good utilization of bandwidth and also since

packets are flowing across WAN, if a failure occurs we are at loss of sending less data. However

once the WAN connection is established, the backups/restore would resume due to resiliency feature.

2) It is also recommended to enable Checkpoint along with resiliency.

3) CD + Accelerator: NetBackup Accelerator significantly reduces the amount of resource (time,

network, and storage) that a full backup requires. Using NetBackup Accelerator, a very large file

system can be fully backed up in the amount of time previously taken by an incremental backup. This

clubbed with CD and WAN resiliency would give optimum utilization of resources.



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Conclusion

WAN resiliency feature provides an efficient way to perform Backup/Restore operations in a typical WANenvironment. This helps to reestablish broken network connections and continue with the operation withoutany loss. The important feature of resilient jobs is that administrator need not have to re start the failed jobsdue to network interruptions. It automatically restarts/continues with the job once the connection is reestablished over the WAN which means the job is still active and is resilient to WAN interruptions.

References

1) Symantec NetBackup Deduplication guide.

2) For statistics on real high availability numbers

http://www.internetpulse.net/Main.aspx?xAxis=Destination&yAxis=Origin&zAxis=Metric&nAxi

s=Period).

3) High Availability Network Fundamentals –

E book by Chris Oggerino.

http://www.internetpulse.net/Main.aspx?xAxis=Destination&yAxis=Origin&zAxis=Metric&nAxis=Period







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About WAN Resiliency