I often steal storage in another area. I will often keep unallocated 2 LDEVs per Array Group in case we need to migrate LDEVs to them using Cruise Control/Volume Migrator in the future.

I’ve been caught out in the past with hot Array Groups and wanting to migrate some LDEVs to cooler AG’s only to find that there are no free LDEVs to migrate onto.

I guess this “could” come under the storage admins lead time buffer that you mention. However, I will always try and keep these 2 or 3 LDEVs free if possible.

Oh and if AG’s are generally hot I may keep more free to keep the IOPs demand on the underlying disks from overloading the disks.

And finally, I recommend and even have customers recommend to me that certain perfromance sensetive applications require their own AG’s. E.g. Ive done some work for a customer who has AG’s dedicated to Exchange Data and other to Exchange logs. They have tons of free space on them that will only be used as the Exchange environment gorws. And even then only up to a certain performance limit within the AG.

It seems there are endless pits or “black holes” into which we throw our storage

Nigel