Magnetic Library Defragmentation

  • 6 February 2021
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I have read a couple or articles on CommVault Online that say defragmentation of the Magnetic libraries is a good idea. Diskeeper, now Dymax IO, was listed as a certified product for online volumes. I am wondering if others defrag theire libraries for performance purposes, and what products they use. I have read in older articles that the native windows defragmentation tool can be used. Also it states that it should be done outside of backup hours (makes sense). Any feedback or information would be appreciated.

 

Thanks


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Thank you for your question.

I can confirm that defragmentation is indeed used by other customer to assist with library performance.

Apart from Disk Keeper, customers usually keep to the native windows tool.

Fragmentation Analysis in this page gives a little more information on the subject: https://documentation.commvault.com/commvault/v11/article?p=9319.htm 

 

 

 

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Hi Monty. What kind of Storage do you use? If you are on a external SAN-Storage or a local RAID-Array I would caution against using Defragmentation Tools, same with SSD/Flash Storage.

On local standalone Disks defragmentation can help. In my Envs we decided to skip that step for now and rely on Commvaults use of Sparsefiles and defragmenting those files if they get too sparse. If you use that external defrag can be contraproductive. 

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@CSumner ...Do you know if the native Windows Tools can be used while library is online or does the library have to be taken offline. Ideally I would like to run the defrag while the Aux copies are running to tape during the day.

 

Stefan… The storage that we are using is external SAN-Storage. So from what you are saying the defrag process can interfere with the CommVault clean-up process?

 

Thanks for all your help...

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you should never defrag SAN-LUNs, that only causes massive load on the Storage without doing anything for performance. Storage Boxes manage the logical blocks themselves and use their own logic to keep access fast.

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you should never defrag SAN-LUNs, that only causes massive load on the Storage without doing anything for performance. Storage Boxes manage the logical blocks themselves and use their own logic to keep access fast.

I agree with this. The way that deduplication works means that you’re going to end up with 99% fragmentation at some point - we granularly remove blocks between other blocks of data which is a natural cause of fragmentation (unless your storage target does not support sparse, in which case you need to run commvault defragmentation anyways (aka space reclamation). How different storage targets deal with fragmentation is going to depend on the target.

If you have direct-attached disk which is not great with random I/O, then you could improve read performance with defragmentation. As Stefan mentions, there are some really smart arrays out there where defragmentation won't make much of an impact, since they already cache or tier hot blocks or restructure data on the backend to optimize access.

 

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Does the Disk Defragmentation give a good result when the maglibs are provisioned out of Netapp NAS?

 

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Hi @SHASHA , We used to have many Netapp FAS2554 NAS and windows defrag is useless in that case, as our volumes were not mounted like a local volume, but really shared with multiple MAs.

Inside the Netapp, we had multiple aggregates and each one could be defragmented using the very long Netapp process (https://library.netapp.com/ecmdocs/ECMLP2502822/html/GUID-93D5DAC1-2147-44EF-B1A9-76E8600AF6F8.html

We tried a few times and it took weeks or months to complete, causing degraded performance during the process, with so little improvement that we decided to never defrag again. 

As @Damian Andre explained, if you’re using Commvault’s deduplication on your disk library is, then it’s also not needed and.

If you have a locally-attached ‘spindle’ disk library, like internal disks inside your server, then you can defrag. 

I pay more attention to have the dedicated volume where the DDB is hosted to be defragged to speedup the backup process, as well as the one hosting the Indexcache.  

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