Save and Claim the lost storage space with thin provisionning

Thin provisionning is a subject which passions me a lot. So when I saw an article written by Gabrie van Zanten. I read carefully to see if I find something that I do not know about. Believe me, I found a good stuff you’ll want to hear about. Gabrie is an experienced virtualization architect.

For persons which does not know much about Thin provisionning. When you create thin provisioned disk in ESX 4 server (let’s say for example 100Gb) it does not take 100Gb place on your SAN. It takes few Mb. Then only when you start store more and more files, this disk will start to grow.

Let say you’ll use this disk as a storage disk and you’ll want to store all your personnal collection of MP3 files there. (crazy non?).You will eat then let’s say 40 Gigs of space. Then you’ll decide to delete some of the Albums you never listen to, so you free 10 Gigs. But you see that the disk does not get back to 30 Gigs. Why? That’s where I saw the explication from Gabe….

“Once a thin-provisioned disk grows, it won’t shrink. This is not because of limitations on storage or vSphere level but because storage and vSphere don’t receive the information that those blocks are empty. Windows does not delete a file when you delete it; it just updates the master file table and registers that block X to Y is now again available for writing, but the space isn’t emptied. This is why neither vSphere nor storage knows that the block can be reclaimed. “

The main advantage over flat vmdk images is that possibility of starting small, even if the Virtual machine see the disk as a 100Gb disk. In my “lab”  I’m using VMware Workstation to test stuff at home, so as Gabrie said in his article, I went to get the tool from Mark Russinovich, I put it on my c: drive, and i run a command: sdelete.exe /? to see what’s the options.

Then I took a snapshot of my VM… (you never know).

Then I runned the sdelete command and the process started. It took about 20min to finish.

Well, then I could not do a Storage vMotion as Gabe recommends… -:) I would have to setup the whole ESX 4 infrastructure on my laptop…. But this might come sometimes in the future…

Technorati Tags: Flat VMDK, thin provisionning, Vmdk, vSphere thin provisionning

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