Defragging vmdk files... performance increase?

I doubt I can give you an authoritive answer but I'll give you my thoughts.

1.  You may get some additional performance gains from the array due to pre-fetching alogorithms but I expect it to be negeglible.

2.  The OS will get some slight performance increases as it can also pre-fetch data perhaps easier.

3.  If you are using virtual pools and thin provisioning, defragging will make your volumes go thicker.  We've tested this at our site.

Either way, I don't think it's worth it at all.

I didn't think about it making it thicker.  I guess this would be due to it using the full space to do the actual defragging?   I was on the fence as well on the performance and believed it would be slight if even noticeable.  Thanks.  Anyone else?

The points listed by Ryan are definitely valid for VMDK/filesystem.  The impact is going to depend a lot on the characteristic of the disk access.  If you deal with it on the extreme spectrums, a highly random read/write load will not benefit from defrag, a highly sequential read will benefit (if severely framented), and a highly sequential write will not benefit as much.  This can be boiled down to how cache impacts the backend operations of disk access in a storage array.

In summary your big winner for defragging is going to be felt in the most traditional and older environments with low amounts of r/w cache, not thin provisioned LUNs, not thin provisioned in VMware, and high sequential reads-- so net/net the impact of doing a defrag most likely will yield less benefit and more performance impact during the operation than its worth.

Anecdotally, there are some software tools that can defrag a drive, zero out the free space so that it's fully reclaimablable by the storage subsystem, and then keep drives from becoming fragmented.  I've toyed with this but the cost has never worked out.

We're migrating from a thick dmx3 environment to a fully thinned vmax system.  We'll probably run sDelete -c on everything prior to moving them to the VMAX to reclaim the space.  Adding in a defrag in that proces if automated wouldn't be the end of the world and you'd net the most savings.  I'm not sure if you've defraged a Win2K3 filesystem lately but so much of it is open files/system files that can't be moved so it never looks very clean anyhow.

Just doing some clean-up.

Moving this discussion to the top-level of the Community where it should be.

        -Dave

In general, it is NOT necessary to do "defrag" using third party tools. More details can be found

http://blogs.vmware.com/vsphere/2011/09/should-i-defrag-my-guest-os.html