vsphere thin provisioning' pros and cons

Thin provisioning allows you to create a VM that thinks it has say 100GB of drive space (or whatever limit you set), but on the SAN storage it might only be using 20GB.  As the VM adds more files to the virtual drive (vmdk file) that drive will consume more on the SAN, until it reaches the 100GB limit that you set initially.

The benefit is that you don't use up all your SAN space as quickly.  Many times you might build a Windows server and give it a 40GB C: drive, but in reality it is only using 12GB or 15GB of that space.  So why should you have 25GB of empty space that you can no longer use on your SAN?  Who knows when that Windows VM will ever get to the full 40GB that you allowed?  You might be able to fit as many as 3 times as many VM's on your SAN using thin provisioning.

The drawback is that you can very easily over-provision your SAN.  If you have a 100GB SAN, and you build 5 VM's, each with a 40GB drive, thin provisioned, they will fit on your SAN easily, and you might even have space left over.  However, as those VM's add files, their vmdk file can grow to the 40GB that you originally allocated.  If all 5 VM's grow to their 40GB limit then whoops!  You're trying to use 200GB of space on your 100GB SAN, which just doesn't work.

It can be a good tool, but you need to be aware and be careful not to over-provision your SAN by too much.

Hi Thomasdietrich:

Thanks for your input.

Will there be any performance issue that may occur if we go thin provisioning?


Thanks