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Has MAID got it made?

Simon Sharwood

It's axiomatic that the amount of data never stops growing. That's why most organisations add more and more disk each year. As they add disk they also add complexity as different tiers of storage bring new machines into the data centre.

Another side effect of storage growth is increasing power consumption.

Vendors have responded to the latter with a slew of announcements about "green" wares.

But one response to the situation is perhaps as simple as can be: why not turn off the disks you don't use!

One implementation of this response idea is called MAID - a Massive Array of Inactive (or Idle) Disks.

MAID is not rocket science. The technique suggests that you turn off your disks when you are not using them.

One application for MAID is within a traditional storage array, with some disks treated normally and others subjected to MAID rules. Always-on disks are considered tier one, with MAID-ruled disks used for secondary or tertiary storage, a role in which it makes sense to switch them off.

Another use is in disk-based archives, a scenario in which SATA disks are preferred, despite their short mean time between failure (MTBF), because they simply won't be running long enough for MTBF to become an issue.

That usage pattern helps make MAID a competitor for tape libraries as an archival technology on reliability grounds. And even though it can take ten seconds to spin up a disk so it can once again deliver data, ten seconds means MAID is a strong competitor for tape on the speed front too. This makes MAID as a useful contributor to tiered storage and information lifecycle management efforts too.

Add in the fact that MAID arrays are also a nice shade of green - switching off unused drives means power consumption is well below that offered by traditional disk devices - and the standard seems to offer a more-than-useful option to the storage professional.

Yet despite these are powerful arguments, MAID is seldom-deployed and more or less unknown.

One reason is that there is no MAID standard. Vendors like Copan Systems have made MAID an integral part of their storage systems, but have done so alone.

Hitachi Data Systems' Marketing Manager Tim Smith advanced the lack of standard for the reason his company does not 'oficially' use MAID, but says the company's products use MAID-like practises as part of their tiered storage implementation that sees some third tier disk spun down when not in use.

Others, however, are starting to promote MAID. Fujitsu, for example, recently introduced MAID into its Eternus 4000 and 8000 SAN arrays, making it the first vendor to use the technology in a mainstream storage device. The company says power savings of 25% are on offer, advancing this figure as the main reason for adopting the technique.

But not everyone is convinced that MAID is truly useful, at least as an archive, questioning why users would want archives that remain online, or 'as near-line' as a spun-down disk.

"The feedback I'm getting is that the dollars do not work out," says EMC's Clive Gold. "It does not work for long term storage and for off-line, tape is still considerably less expensive."

"So my take right now is that MAID is a solution looking for a problem."