Clariion – Storage Pool oversubscribed

Hi James,

Oversubscription is not a bad thing. If anything it's a sign you're saving a lot of money: if you would NOT have used thin provisioning you would had to buy all that capacity in advance!

The thing to be aware of is that the pool never fills up completely. If the pool runs out of space you're in trouble since your LUNs will go offline since there's no more space to write new data. So make sure you have your hardware purchase processes well in order and that you can order additional disks once you need them.

The company I now work for has some serious difficulties getting hardware on demand, so that was a big reason for us to NOT use thin provisioning (e.g. not oversubscribe). I'd rather spend some more money on disks which I can keep online for sure, instead of saving a couple of K and having nightmares of procurement holding back our disk order when the pool is approaching critical mass...

I'd advice on not going completely overboard with assigning capacity to servers/users. Challenge your customers: if they request 1TB, it is likely they only need it in a couple of months and are only requesting it now since they're afraid they can't expand when needed. Maybe they can live with 500 or even 250GB initially, and then grow it every couple of months.

This approach will keep your data to "allocated space" ratio in order. If you have 10 customers, all with 1TB LUNs that only use 100GB, you're in trouble once they all decide to fill the remaining space with X-mas videos...