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Device Streams
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Post Device Streams 
Hello -

What dictates the # of device streams setting for a storage policy?

Our maglibs mount paths allocation policy are all set to 'maximum allowed writers'

From CV's documentation below, can someone clarify 'sum of drives available and/or the sum of writers...'? Is it the physical # of hard drives that make up the LUN? Is it the total # of mount paths for all libraries (used as alternate data paths)? Also, we just changed the device streams on our storage policies for file system from 5 to 10 to see how it goes (as a lot of the jobs were queued over the weekend as the storage policy could only handle 5 streams). How will the system behave if, let's say, we bumped it up to 20, or even 30, device streams?

Thank you.

From CV's documentation below:

"If alternate data paths are added, it is recommended that the number of streams must be equal to the sum of drives available in all the libraries and/or the sum of writers in all the magnetic library/mount paths associated with all the data paths."


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Post Device Streams 
If you're dealing with tape, that's where the # of drives makes the difference. In dealing with MagLib, you're really just trying to find the number where you're getting your optimal read/write speeds. Adding more doesn't get you anything, reducing the number reduces the total write speeds.

In my environment, I have the maglib set for max, but then I use Storage Policies to limit the # of jobs. What was happening was that I had a large amount of WAN backups and because they ran so slow, some LAN jobs here would be stuck waiting while slow WAN jobs ran. So I have a storage policy for WAN jobs and I allow 90 jobs at once to run, because even 90 jobs at one time from the WAN doesn't amount to a lot of throughput. But the LAN jobs, I limit them to about 25 per media agent. This number comes from how many jobs until I see its NIC hit 100% from incoming client data and how much data my disk can write comfortably.

"rickyv87" <rickyv87 < at > yahoo.com> 1/3/2011 10:22 AM >>>

Hello -

What dictates the # of device streams setting for a storage policy?

Our maglibs mount paths allocation policy are all set to 'maximum allowed writers'

From CV's documentation below, can someone clarify 'sum of drives available and/or the sum of writers...'? Is it the physical # of hard drives that make up the LUN? Is it the total # of mount paths for all libraries (used as alternate data paths)? Also, we just changed the device streams on our storage policies for file system from 5 to 10 to see how it goes (as a lot of the jobs were queued over the weekend as the storage policy could only handle 5 streams). How will the system behave if, let's say, we bumped it up to 20, or even 30, device streams?

Thank you.

From CV's documentation below:

"If alternate data paths are added, it is recommended that the number of streams must be equal to the sum of drives available in all the libraries and/or the sum of writers in all the magnetic library/mount paths associated with all the data paths."

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What dictates the # of device streams setting for a storage policy?

There are a number of places that you can adjust the streams. For a MagLib you want to limit the number of streams to the number of spindles minus 1. In my case I have 5 LUN's presented with 6 spindles for each LUN. So I could allocate up to 5 streams per LUN, but I only allow 2 per for best performance (I use 2TB SATA drives).

I have a shared storage policy with 80 streams, my MagLibs are all set to spill and fill, each Drive in my MagLib's is allocated 5 streams, and each agent subclient is allocated 10 streams. For my VMDK backups this works out to average 2 streams per Drive (LUN). Gives me my best performance.

You will have to adjust each part until you get to your best performance. I know it gets complicated but with CommVault's granularity you can really tweek for performance.

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