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How to throttle CPU and network usage of anAvamar client during backups

Symptom:

An Avamar client requires memory, CPU and network resources in order to perform a

backup.

 

The amount of memory required is dependent on the Avamar client's cache file sizing. By

default, the Avamar client's avtar process will use as much network bandwidth and CPU

cycles as are made available to it by the operating system.

 

CPU Utilization

If a backup runs during a time of day where the client machine is under heavy production

load it may be considered desirable to throttle avtar's CPU utilization in order to ensure that

CPU cycles remain available for other system services.

 

Avtar CPU utilization can be reviewed in the Avamar client backup log as shown below:

 

avtar Info <5100>: Status 2009-04-10 20:37:02, 0 files, 25.00 GB (0 files, 473.7 MB, 1.85%

new) 117MB 99% CPU

 

Network utilization

If an Avamar client is located remote from an Avamar server via a low bandwidth link it maybe desirable to throttle network utilisation under certain circumstances.

 

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Cause:

Avtar's usage of CPU cycles and network bandwidth is not restricted by default. This is

normal and expected behaviour as it is usually most desirable that Avamar backups run and

complete as quickly as possible.

 

Resolution:

The following flags exist to throttle network and cpu utilisation of the avtar process:

--throttle (throttles network usage)

--cpu-throttle (throttles CPU usage)

 

To implement either of these flags, edit the avtar.cmd file found in the Avamar client's avs/ 

var directory. Create a new avtar.cmd file if one does not already exist.

 

CPU Throttling

The entry made in the file should be in the following format, where '80' is the maximum

average percentage of CPU that the avtar process should use.

 

--cpu-throttle=80

 

Network Throttling

The entry made in the file should be in the following format:

 

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--throttle=MBPS

 

When implemented, avtar will pause as long as necessary after sending each packet in

order to ensure that network usage does not exceed the specified maximum bandwidth(specified in mega bits per second)

 

For example, --throttle=5 uses half a 10Mbps connection, --throttle=0.772 restricts usage to

one-half of a T1 link.

 

After making the changes, save the avtar.cmd file.

Restart the client agent from the client GUI (Operations > Advanced > Restart Client

agent, in Windows) and run the backup.

 

CAUTION

1. Processes normally run as fast as they can. If we attempt to lower the CPU utilisation of

the client processes, then the backup may run MUCH slower than it otherwise would and

may not complete in time for the backup window.

 

2. If we slow down the process, other clients which are queueing to start their backups will

be delayed by the lengthened backup time of this client.

 

3. If the client is performing other work at the time of the Avamar backup, this work will be

impacted less but for a longer period of time.

 

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4. If in doubt about the suitability of applying the flags discussed below, contact your EMC

Professional Services representative.

 

Please refer to Knowledge Base article esg95533 for detailed explanation.