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defrag VM on a san lefthand

Frequent Advisor

defrag VM on a san lefthand

i had a server data (windows 2008 R2) host on my san,
yesterday i read in the lefthand documentation that they recommanded not to defrag the file system ?

But for me as it is a data file server if i did'nt defrag it regulary i would have slow down time

what is your opinion ?
Patrick Terlisten
Honored Contributor

Re: defrag VM on a san lefthand


defrag is nice for single disks to align the blocks, but in a SAN, with a storage system and multiple disks, the blocks are distributed over many disks/ storages. In an enviroment with many servers, logical drivces and physical disks you can't align the blocks.

Best regards,
Uwe Zessin
Honored Contributor

Re: defrag VM on a san lefthand

You can align 'blocks' ... somewhat at the physical level if the file system block size/ 'cluster' size is smaller than the storage array's chunk size and on the file system's logical level which can result in less I/Os.

Here is some interesting reading:

But every environment is different, so the best is if you can try it out.

One warning though: the recommendation not to run defragmentation mostly refers when one is using thin-provisioning or snapshots/smart clones on a volume.

Defragmentation makes volume changes - not good for snapshots - and it can write into previously untouched areas - not good for thin-provisioning.
Frequent Advisor

Re: defrag VM on a san lefthand

thanks for all the documentation

after reading all those documents, i was not sur for what to do
so, i choice to stop for the moment the defrag and i will search more about.

For information i had a VMWARE VM Windows 2008 R1 on a thin provisionning volume on a san lefhand

jason andrade
Frequent Advisor

Re: defrag VM on a san lefthand

defragging made sense to me when you had locally attached spindles and usually no raid involved.

filesystems were also a lot more primitive back then.

with the advent of raid and then SANs where you have moved to dozens and hundreds of spindles, trying to realign blocks didn't really make sense anymore.

in addition a lot of filesystems now seem to do built in defragmentation.