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Need info on option "Maximum I/O streams per volume"

Created: 14 Nov 2012 • Updated: 30 Nov 2012 | 2 comments
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Hello Everyone,

Would appreciate if anybody can give me detailed information on "Maximum I/O streams per volume" in Netbackup using SLP.

It'll be great if it can be with Example.

Environment:

Netbackup 7.1.0.1 & Windows Server 2008.

Thanks in Advance

Hemant

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Nicolai's picture

From the Netbackup 7.5 SLP best pratice manual:

http://www.symantec.com/docs/HOWTO73205

 

Use “Maximum I/O streams per volume” with Disk Pools
Disk storage units allow you to limit the number of concurrent write jobs that use the storage unit, however there are no limits on the number of read jobs (restores and duplications) that may be accessing the same disk pool at the same time and it is also possible to configure multiple storage units to access the same disk pool simultaneously. This can give rise to unexpected I/O contention on the disk pool. By setting the Maximum I/O streams per volume option on the Disk Pool, you can limit the total number of jobs that access the disk pool concurrently, regardless of the job type. While the disk pool is maxed out with backup jobs that are writing images to the device, no duplication jobs are allowed to start reading from the device. (The one exception to this rule is that restore jobs are allowed to read from the Disk Pool even if the maximum configured number of input and output streams is already being utilized.)
When you enable the Maximum I/O streams per volume option on the Disk Pool the default number of streams is 2. Although the optimal number of streams per volume will vary depending on the disk type, a general guide line to minimize contention would be to divide the maximum concurrent jobs count for all the storage units using the disk pool by the number of volumes in the disk pool.

Assumption is the mother of all mess ups.

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SOLUTION
RonCaplinger's picture

If you are using a disk appliance, such as a Data Domain or other device, there is likely an admin guide or manual that will tell you the vendor's recommended maximum number of streams.  You should follow their advice, as there are multiple factors that can affect the number of streams, including the appliance's CPU, memory, etc.

For instance, a Data Domain model DD670 with 16GB of RAM can handle 90 write streams (backups), 30 read streams (restores), or 60 replication streams if it is the replication source.  If the memory on the DD670 is increased to 36GB of RAM, it can still only handle 90 write streams, but now 50 read streams or 90 streams as the source for replications.

I set my # of streams below the max number of write streams, as I have seen some backups fail intermittently when set exactly to the above numbers.