SATA disks are fuelling the advent of disk-to-disk backup with its elimination of the backup windows and virtually instant restore. SATA disks are also used to store fixed content data as with EMC's Centera and StorageTek's BladeStore. But SATA disks' reliability is a concern and an array of hundreds of spinning disks is not cheap. Think of all the power supplies, cables, cache memory and controllers needed for each drive.

A US company called Copan Systems has a new spin on this. Treat the disk drives as tapes in a library and only have them powered up when needed, hence the massive array of idle disks idea. A Copan array will contain hundreds of terabytes of disk in a single cabinet (think bladed disks). Copan claims it will be able to offer disk backup at tape prices because of the savings involved.

The many hundred disks share a power supply/controller/cabling cabinet infrastructure.

An algorithm is used to decide which disks in a cabinet should spin and which not. Inactive disks are powered down and then spun up again when needed. Reactivation typically takes under 10 seconds. Disks are spun on a regular basis even when not used to keep them operational. This so-called duty cycle management can reduce the number of stops, experieced by a drive, by a quarter. For comparison a typical ATA drive is built for 40,000 stops over its life.

Randy Kearns, a partner at the Evaluator Group, says, "They're really creating a disk library instead of a tape library. You spin them up and use them when you need them, just like tape."

There will be some form of RAID-like scheme to recover from disk or data loss. MAID arrays will be used to store fixed content data as well as backup sets, according to Copan. They wont quite be MAIDS of all work.

Other suppliers offering MAID arrays include Asaca, with its digital virtual libraries, and Exavio with its ExaVault containing storage trays that can be individually spun up or powered down. StorageTek is also apparently talking about a hybrid disk and tape unit.

MAID products are appearing in the USA now. It will take some months, and some courageous resellers, before they become available in the UK. When they do, remember, you read it here first.