Disk array supplier EqualLogic has added 'thin provisioning' to its PS products. That should make its PS array products more economical to buy. This follows on from LeftHand Networks having the feature in several generations of its SAN/iQ software.

Usually an application is allocated XGB of storage, say 50GB. But this is what it will need over time as it writes data. What it might actually need in the first six months is 5GB. Thin provisioning tells the app it has 50GB available but only puts aside 5GB. When that fills up the app is given another 5GB and so on. Across a bundle of apps this means you don't have to buy so much storage up front and so save money.

Array suppliers like 3PAR have had this feature for some time. HDS, and its OEM HP (and, presumably its OEM Sun) are adding it to the enterprise high-end array product area. Now it is becoming a general feature of the iSCSI storage space too, that is file and block storage accessed over Ethernet rather than Fibre Channel, at first with LeftHand and now EqualLogic. It will be a standard feature of EqualLogic PS arrays, needing no additional license. Thin provisioning can be switched on and off at the volume level enabling trial runs and flexibility with application needs.

EqualLogic's implementation includes proactive, user-defined threshold alarms and controls on automatic space allocation that minimize the possibility of a “run” on storage that could fill capacity of a thinly provisioned SAN.

The EqualLogic release quoted Ken Kaban, European technology services manager for Foster’s EMEA, currently testing thin provisioning on PS arrays. He mentioned a few topical topics: “The addition of thin provisioning will allow us to plan our storage infrastructure needs for the next five years, which previously would not be possible without wasting significant amounts of time and resources. It will also reduce the amount of space required in the data centre, saving us on power and cooling costs.”

John Joseph, EqualLogic's marketing VP, banged on the 'no additional license fee' drum, and why not? “Our offering of thin provisioning ... for our customers ... means they don’t have to pull out their wallet when they want to add software for replication, snapshots, tiering, or when they’ve filled the capacity of their thinly provisioned volumes and need to buy another license.”

The iSCSI storage space is rapidly maturing.