Microsoft revives MAID with Pelican, but tape can still sleep easy

A decade ago storage journalists were quite keen on a new technology around at the time. That was MAID – Massive Array of Idle Disks – which were basically disk-based backup target devices with lots of drives that could be spun down when not in use and so were suited to infrequently-used data.

The key attraction was access times quicker than tape, but avoiding some or most of the cost of powering and cooling lots of hard drives. A UK company called Copan was a pioneer of this, but lots of mainstream and lesser-known storage box makers got on board for a bit.

By the turn of the decade Copan had been swallowed up by SGI and MAID seemed to run into the sand. A range of explanations were proffered, that ranged from the unsuitability of HDDs to power down and up to the simple economics of still not being as cheap as tape.

But, Microsoft is rolling out its own MAID-like array to its Azure datacentres, according to CTO Mark Russinovich in a presentation in Sydney this month.

It’s called Pelican and it weighs not far off a tonne and a half. Packed with 1,152 10TB drives in a non-standard 52U rack it can store up to 11.5PB.

The idleness of drives therein is enforced by the dual controllers (that also contain its object storage file scheme) that schedule and orchestrate spin up, spin down, rebuilds etc and the key operating principle that no more than 8% of drives can ever be spinning, which is what keeps Pelican within its cooling parameters.

Pelican is being developed and rolled out by Microsoft for its Azure cloud datacentres, and is explicitly only for those that are “not big enough” for tape infrastructure (Azure currently uses IBM TS3500 libraries), according to Russinovich.

Implicit in that, it seem, is an acknowledgement that even today’s MAID, with 10TB hard drives and massive density, still doesn’t compete with tape in all scenarios. If it did, Microsoft would roll it out to all their Azure datacentres and we’d be set to see it hit the wider market.

So, for now, tape may not be dead. And can rest easy for the time being.

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