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I've got about 60 servers that were migrated from physical machines running on ESX 4. I'm having issues with the Diskeeper software installed, and I'm trying to decide if I should try to fix the software or just disable/uninstall it. Any need to defrag VMs?

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up vote 4 down vote accepted

You should defrag VM disks in the same way and for the same reasons as you'd do so on physical servers - file systems still fragment the same.

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There shouldn't be a need to defrag the disk-images on the VMFS side, but inside the VMs themselves fragmentation can still be an issue.

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This is a very good point 1138, but then I got to thinking about if you extensively use Thin disks, they're bound to effectively fragment eventually I'd have thought (well if they expand periodically anyway) - as far as I know there's no way to 'sequentialise' these 'live' is there? – Chopper3 Nov 15 '10 at 17:29
@chopper3 I forgot about thin... So far as I can tell, the only way to sequentialize a Thin VMDK is copy it to a new LUN. Unfortunately, I don't know enough about how VMFS works to guess at what kind of frag-penalties it suffers. – sysadmin1138 Nov 15 '10 at 17:45
@1138, yeah, that was my point I guess - it's often overlooked, my myself if nobody else. To be honest I rarely use 'thin' in production but do use it a lot on dev/test systems where I don't really care if fragmentation does have an impact to be honest. As for how it actually works, well I don't know for a fact but I do know a particular .vmdk (well it's hidden storage bit anyway) will grow sector by sector as it's filled up, obviously if you have two or more of these growing in an 'interleaved' fashion then that'll be replicated on the actual disk -but there's a limit to how concerned I am :) – Chopper3 Nov 15 '10 at 18:10

A Thin privisioned disk scatterd around a LUN is not a big problem, because the VMFS kernel allocates around 5MB for each time the VM hit's the limit. So in a worse case scenario you have A1 B1 A2 B2 A3 B3 each being around 5MB in size. Your harddrive solution will probably won't decrease a lot of performance hopping the disk head each 5MB. It will affect performance a little but not that much.

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As I understand it, the Diskeeper app you were using called V-Locity defragments the guests but not the host. A colleague of mine wrote into their Support for help with the same application and said they were good about getting him some help with it. You might consider contacting them.

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