Just got word that I’m going to be doing a “Thin Provisioning” install next week. I’ve not had a lot of experience with EMC’s implementation of this particular brand of virtualization so it’s going to be interesting.
Thin provisioning has been around for a while, I think NetApp and Compellant have had thin devices in one form or another, but it’s not my idea of a fun time.
Thin provisioning is basically pretending you have space that you don’t. You create a storage pool, or a group of volumes that your “thin” disks can pull from, they fill up space as it’s used, taking from the pool of disks in the process.
The thin devices then pull from the common pool as tracks are used. This way a 500GB pool of disks can easily be provisioned to the hosts as a terabyte or more of virtual disks.
But if you create a 500GB pool and 4 250G “thin” devices, you are only safe until the total used space hits 500GB. (IE 125G in each thin device)
I can’t even begin to count the number of ways this can blow up on you. The only reason for using thin provisioning would be to lie to your internal customers. Now granted I can think of a great use for this in dealing with users who make unreasonable storage requests. (You know, the “I need 250GB for a webserver that only has a 35MB webpage hosted on it” types)
The problem is, again. When they decide to fill up the disk, you’re out of luck.