It turns out 3PAR needed a bit of help to get its fat-to-thin process working properly.
The latest T-class InServ storage array has clever hardware that turns an incoming fat volume into a thin one. This means that if you migrate a storage volume from some other array that does not have thin provisioning - a fat volume - then it automatically becomes a thin volume on the T-class because its contents pass through the hardware and repeated zeroes are stripped out, leaving just the actual written data in the volume.
That's lovely, only it isn't totally and ecstatically lovely because some of that written data could be deleted files. In fact quite a lot of it could be deleted files. Slow operating systems like Windows take shortcuts to keep the speed up. When they delete a file they sprint off to the disk, set a delete flag in the file header, sprint back again and say: "What's next?" without actually deleting the file at all. So it's full of data bytes instead of zeroes.
Cue migration to the T-class Inserv, and this Windows laziness completely defeats the fancy new 3PAR hardware which doesn't know a deleted file from a pain in the rear, which it is.
So 3PAR has got together with Symantec and its latest Veritas Storage Foundation volume manager product. What you do is use Storage Foundation's SmartMove to migrate the storage volume to the T-class. It detects the delete flag in files in the volume and doesn't send them to the T-class. What a smart move.
Symantec has also announced a Thin Reclamation API which can be used to trawl thinly-provisioned volumes and remove all the space taken up by deleted files. It returns this space to the array's central pool, thus ensuring your thin volume remains at its anorexic thinnest. You just run the thing every so often, much like defragging a PC's hard drive. Neat.
Symantec's SmartMove and Thin Reclamation API work with any thinly-provisioned storage array in principle. 3PAR is Symantec's first storage array partner to use it with HDS and HP issuing approving quotes in the Symantec release. They'll have it available as soon as they can get their array software working with the Symantec software.
Both SmartMove and the Thin Reclamation API are included in the latest version of Storage Foundation. It's available now and costs $695 per server. Um. So if you have 1,000 servers that's $695,000. Better not thinly provision your wallet. ®