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vCloud Director Storage Allocation with Thin & Fast Provisioning

This has been something I've been meaning to get to the bottom of recently. When you give an Organization vDC storage from a specified Storage Profile, how does that react to VMs that have been provisioned with Thin or Fast? If I allocate 200GB to an Organization vDC, where does it get capped?


If you have provisioned a lot of VMs before, we may have seen this screen: The requested operation will exceed the VDC's storage quota.





I wanted to dig around so I created multiple Pay as you go Organization vDCs with the same CPU and RAM quotas and guarantees. 0 and 0.


In each case I allocated 200GB of the Storage Profile to every vDC


My test VM is a Windows 2008 R2 image that is Thin Provisioned. vCloud Director displays its disk consumption at 60GB, but the actual consumption is only 10GB.


So my first test was to use an Organization vDC that was using both Thin Provisioning and Fast Provisioning


I created my first VM and it was only using 10GB of actual storage. Exactly what I was hoping to see.


I know that I have 200GB of allocated storage. How many more 2008 R2 VMs can I spin up? If they are only consuming an actual amount of 10GB, I should be able to spin up 19 more. If the calculations being used are of the "potentially provisioned" size, then I should only be able to spin up 2 more VMs, giving me a total of 180GB of potentially consumable space. Therefore, if it try to spin up 3 more VMs, which is a total of 240GB of space, then it will fail. In my testing below, we can see that vCloud Director takes the latter calculation of "potentially usable space". When trying to spin up 3 VMs, I get the a failure that my Organization vDC cannot support it and the storage quota will be exceeded.  That was a pretty simple problem to solve. It doesn't matter if I enable or disable Thin or Fast provisioning, the storage quota will be dictated by the size of disk on the VM itself.


To keep things interesting, I wanted to see what happens in other scenarios:


If I disable both Thin and Fast Provisioning, then the VM deployed is consuming an actual usage of 60GB.


If turn off Fast Provisioning and Enable Thin Provisioning, the VM is consuming an actual usage of 10GB.


If I turn on Fast Provisioning and disable Thin Provisioning, the VM is consuming an actual usage of 10GB. I found this one particularly interesting because even though I'm telling it to not use Thin Provisioned disks, the Fast Provisioning aspect still makes the VM use the original base image which was thin provisioned. This may be a symptom of the base disk being used for other Organization vDC's prior to this testing, but strange nonetheless.

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