Thick VM with thin SAN?

blinkme323
blinkme323 used Ask the Experts™
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Hello,

We are currently running a thin provisioned SAN back-end with a thick provisioned VM environment.  I'm trying to understand how this works / the logic behind it.  Is the SAN essentially saying "I'm going to give VM a logical block, but I will only account for what is used" and then the VM env is saying "oh I have this whole block of storage, I'm going to take it all"?

That is the scenario that I laid out in my mind, but I'm looking for confirmation as to what is actually happening here.

Thanks in advance!
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Senior Infrastructure Specialist
Top Expert 2016
Commented:
Since thick provision lazy zeroed only allocate the space but don't zero it out (like thick eager zeroed does), from SAN it will behave in the same way of a thin provision VM. But from VMware, you will have the space allocated and without risk of over provision the datastore space.

The following blog post explain with some additional examples: http://theithollow.com/2013/03/26/are-you-thin-or-thick-where-at/
Top Expert 2014
Commented:
As far as VMware is concerned it has all the space you gave it, but the SAN will only allocate physical disk space as and when needed. Create a few VMs with data on them and delete them again and you'll soon use up all the physical disk space in the SAN.

Whether the SAN grabs back zeroed out blocks is down to the SAN manufacturer, it probably does but it may only reclaim unused blocks periodically.
Richardson PortoSenior Infrastructure Specialist
Top Expert 2016

Commented:
Do you need any additional explanation or we can close the question?

Author

Commented:
Yes, this can be closed.  Please award full points to each of the commenters as it will not allow me to.

Thanks
Richardson PortoSenior Infrastructure Specialist
Top Expert 2016

Commented:
Enough information provided.

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