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Google calls for datacentre storage disk design overhaul

Search giant Google says an overhaul of traditional 3.5in disks could lower the total cost of ownership and improve infrastructure performance

Google wants the IT industry to join forces with the academic community to create a new generation of datacentre storage disks.

The search giant said this would help web-scale internet companies cope with the petabytes of data users upload to their services each day.

Google published a white paper proposing several design options for datacentre disks, which includes a motion to scrap the traditional 3.5in hard disk drive (HDD) form factor on capacity grounds.  

“The current 3.5in HDD geometry was adopted for historic reasons – its size inherited from the PC floppy disk. An alternative form factor should yield a better TCO [total cost of ownership],” suggests the white paper.

“Changing the form factor is a long-term process that requires a broad discussion, but we believe it should be considered," wrote co-authors Eric Brewer and Lawrence Ying.

“Although we could spec our own for factor (with high volume), the underlying issues extend beyond Google, and developing new solutions together will better serve the whole industry, especially once standardised.”

The company said it would like to see the IT industry invest in taller hard disk designs, with fewer points of failure.

“Current disks have a relatively small fixed height: typically 1 inch for 3.5in disks, and 16mm for 2.5in drives. Taller drives allow for more platters per disk, which adds capacity and amortizes of the costs of packaging, the printed-circuit board and the driver motor/actuator,” the white paper states.

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Moving the read/write cache

“Given a fixed total capacity per disk, smaller platters can yield smaller seek distances and higher RPM, and thus higher IOPs, but worse GB/$.”

The paper also puts forward a case for making the capacity of spinning disk storage more flexible, rather than relying on the use of fixed capacity drives, because of the TCO benefits this could bring.

For similar reasons, the document floats the idea of shifting the read and write cache from the disk to the host, claiming it could work out cheaper and more efficient.

In a similar vein, the company sets out the reasons why it will not use solid state disks (SSD) as a wholesale replacement for traditional spinning storage media for some time to come. 

“The cost per GB remains too high and, more importantly, the growth rates in capacity/$ between disks and SSDs are relatively close, so that cost will not change enough in the coming decade,” the white paper stated.

Growth in data volumes

To emphasise why it's pushing for these changes, Google revealed that YouTube users upload more than 400 hours of video content a minute, meaning the company has to bring online up to a petabyte of storage every day to meet demand.

With the company forecasting an exponential growth in data volumes over the coming years, the way it and other web-scale companies run their datacentres will need to adapt.

“Disks are a central element of cloud-based storage, whose demand far outpaces the considerable rate of innovation in disks. Exponential growth in demand implies that most future disks will be in datacentres and thus part of a large collection of disks,” the paper continues.

“We hope this is the beginning of a new era of datacentre disks and a new broad and open discussion about how to evolve disks for datacentres. The ideas presented here provide some guidance and some options, but we believe the best solutions will come from the combined efforts of industry, academia and other large customers.”

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