One of the exciting promises of thin provisioning, is getting more “bang for your buck” out of the expensive enterprise storage you have been investing in for your ESX environment.  But, as Bret Michael’s once said, “Every rose has its thorn” and there are some things to look out for and considerations to make, before implementing thin disk technologies.

o your homework and make sure you understand the characteristics of the virtual machine that you are considering migrating into a thin disk configuration.  The last thing you want to do is convert every VM to thin disk, and four months down the road all of your data stores are filling up and you’re scrambling for a storage CAPEX.  Some people are of the opinion to do thin provisioning either on the host side (VMware) or on the storage array side, but not both.  Take a gander at Chad Sakac’s blog that discusses thin on thin and some thoughts around each of these approaches.  I’m not going to go into all of the pluses and minuses of thin provisioning but rather focus on how to make it work for you.

Source: http://www.virtualinsanity.com/index.php/2009/10/12/get-thin-provisioning-working-for-you-in-vsphere/