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Hitachi GST plugs its areal hole with shingles

Listens to Google, Facebook as much as HP or Dell

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Hitachi GST, in the process of being acquired by Western Digital, says Shingle Magnetic Recording is a necessary gap-filler before advanced disk recording technologies come on stream. It is currently talking to Facebook and Google about this.

CEO Stephen Milligan said Hitachi GST aims to cover all the storage bases from fast access flash thimbles to big fat spinning data tubs. Although it is a hard disk drive (HDD) vendor it doesn't approach the market just as a HDD unit shipper. Instead, it sees its job as enabling a cloud storage ecosystem that encourages content creation and consumption, by consumers with hand-held devices for example. The more data there is the more data has to be stored.

Hitachi GST is developing future flash and disk storage devices in consultation with stakeholders; its major OEMs, operating system suppliers, and cloud software stack owners such as Google and Facebook.

It's probably best to start from areal density where the HDD industry is having issues that will affect these stakeholders.

Areal density matters

Data content is increasing and disk capacity is growing too, based on areal density improvements. The problem is that areal density advances have slowed. Brendan Collins, Hitachi GST's VP for product marketing, said: "We plan for 30 per cent increases annually currently but we are actually running at 15 to 20 per cent."

Between now and 2016 or so, when post-perpendicular magnetic recording (PMR) technologies such as Bit-Patterned Media (BPM) and Thermally-Assisted Recording (TAR1) could come in and increase areal density up to 5Tbit/in2 and beyond, an area where PMR simply cannot go, there is a gap. Shingle Magnetic Recording (SMR) is a technique to get more tracks on disk platter surfaces.

PMR technology is increasing areal density too slowly, as well as facing a limit as to how far it can go, and the HDD industry needs SMR as an intervening technology to give PMR a helping hand. Collins said: "SMR could get us back up to the 30 per cent annual increase rate... TAR1 and BPM: we're going to need both [and] SMR is the bridge to getting there."

For sure, both BPM and TAR will be needed: "It's not either/or; they are complementary." One will be first and may have a one to two years on its own before the other technology joins it. The problem is that no one knows which one will be first, so HDD vendors have to invest in both technologies.

Shingled magnetic recording

SMR comes with its own issues. It writes partially overlapping tracks to increase a drive's areal density – imagine overlapping shingle tiles on a roof. There is a problem with random writes and deletes though, as the deleted parts of the target tracks are also part of the overlapping track or tracks.

Shingled writing

Shingle Magnetic Recording diagram

That means their contents have to be recovered and set aside, the track(s) marked for deletion deleted, and then the set aside data re-written to the drive. All of this takes time and slows the shingled drive's performance when doing deletes.

Random writes are also problematical. If they are written in free space then files can end up very fragmented with extended read access times. If they are written in the file's existing space, then any overlapping tracks have to be re-written too, thus extending write times. Collins reckons that Hitachi GST has some ideas that could help.

He thinks that archive data storage is a good fit with SMR technology as lots of sequential blocks are written. In general though: "We have to find ways of embedding intelligence into architectures to hide shingle disadvantages."

Getting back to server and client computer code stacks that read and write from hard drives, Collins emphasises that HDD vendors and code stack owners have to work together: "Look at Microsoft: its operating systems are not optimised for SMR. We have to make the [SMR] drive totally seamless to the O/S [and] make it look like a PMR drive... Google and Facebook have their own stacks and are making changes to ensure their software file systems work with SMR drives. We're already having in-depth technical discussions with them."

Milligan emphasised that: "We're talking to all our customers about this. It's incumbent on us to establish the right relationship with all our customers [and ask] how can we be relevant to you?"

Collins said: "The Wintel platform has been a major influence on our product designs for the past 20 years and will be our bread and butter for the next five years. But ARMs and Android devices are opening up whole new opportunities going forward."

Hitachi GST will carry on talking to major Wintel OEMs, such as HP and Dell but, increasingly, Web 2.0 and Internet infrastructure companies, like Google and Facebook, are becoming influential too.

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