Thin Disks - your thoughts?

[vcpguy]

Hi, I was wondering how would a thin disk and defra work? If, I have thin disk and a user runs a defrag OR worst case, if there is a AD policy that will run the defrag every quarter, and all the concerned Vms are sitting on the same datastore won't that cause the VMs to crash due to lack of disk space on the datastore? OR, if the user knows there is a overcommitment of storage and on purpose he runs a defrag, then that can cause a significant problems.

I guess monitoring and being on top of things are very imp in this case?

Any ideas/suggestions as to how to use this technology and at the same time, not to get worried, about potential Timebomb problem ?

Thanks

[vmroyale]

Hello.

Defragging a thin disk will make it grow to varying degrees.  As you said, the monitoring is extremely important here.

Good Luck!

[golddiggie]

Diskeeper (http://www.diskeeper.com/) is supposed to have products that will do a proper job of defragging VM's drives... I've not used them, personally, yet, so I cannot comment on how they work out. In theory, though, something along those lines is probably a better idea than the tools included with Windows.

[WilliamKilmarti]

I work for Diskeeper so I might be able to offer a litte helpful information:

Very good question. Thin or not, the drive will fragment. But if you DEfragment it, the drive will grow. The best solution is not to have fragmentation in the 1st place (as well as you can) and then to defragment prior to any scheduled disk compaction.

Here's VMware's comment:

“For  peak performance of Guest OSes running Windows, VMware recommends Best  Practice maintenance with V-locity virtual platform optimizer, a VMReady  solution. As referenced in VMware KB article Defragmenting a Disk:  “Defragmenting a disk is required to address problems encountered with  an operating system as a result of file system fragmentation.  Fragmentation problems result in slow operating system performance.”  Note: This is Guest-specific. Host -Level Linux FS don’t require  defragmentation.”

http://alliances.vmware.com/public_html/catalog/ViewProduct.php?Id=a045000000F9kfFAAR&productName=V-...

But it's important not to defrag without considering thinly provisioned drives. I'm not trying to pitch it but the reason it plays nicely in that type of environment is that it will handle most fragmentation prior to the occurrence.

V-Locity (2.0) for ESX 4 and 4.1 has a built-in disk compaction tool as well--if that helps.

Hope that helped...

EDIT: In the new release of V-Locity (3.0) the built-in disk compaction option has been replaced by a feature that zeros out free space (ESX & ESXi) and allows the admin to reclaim the free space during Storage vMotion. More data in the attached paper.

Message was edited by: WilliamKilmar…

[golddiggie]

Are the current offerings good for ESXi as well as ESX? At this point it shouldn't matter which flavor you're running/using. 

[vcpguy]

I am kind of confused. Are you telling me that with diskeeper, there will not be a problem of disk growing in size if i run defrag ?

Also, can you please tell us more about disk compaction tool ?

Thanks

[WilliamKilmarti]

Yes and no--sorry for the connfusion.

When it comes to defragmenting a thinly provisioned drive, it can be "tricky" as the drive can grow, out of control, and require compaction and cause whatever problems you can imagine.

Diskeeper corp has two products that work in this type of environment: Diskeeper and V-Locity. V-Locity currently works on ESX 4 and 4.1. The ESXi version should hit the streets in the beginning of July--hopefully...

Diskeeper is natively a defragmenter; it always has been and probably always will. The question is not whether or not fragmentation affects vmdks running NTFS, it's really how to go about handling the problem.

VMware suggests using V-Locity but it's important to remember one main point: defragmenting a thinly provisioned drive can get messy--sorry for the redundancy.

Within Diskeeper AND V-Locity is IntelliWrite. IntelliWrite works at a driver level and simply eliminates MOST of the fragmentation that would have occurred in the first place. So DE-fragmenting becomes much less necessary.

You can defragment those drives but it you would do it keeping in mind that it will cause them to grow. It's not uncommon to compact a thinly provisioned vmdk and so you can DEfragment prior to compacting it to clean up anything Intelliwrite missed. In other words,

I've attached a best practices paper that helps to explain it a bit more.

I hope that helps. Please let me know if I can better clarify that.