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Coughlin's cogitations

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Disk drive capacity increase challenge

El Reg: How do you see the HDD industry solving the challenges of increasing disk drive capacity facing it as current PMR technology runs out of steam? Do you see the transitions to the next technology being (a) Shingled writing or adding platters or both while staying with PMR (Perpendicular Magnetic Recording), (b) then HAMR (Heat-assisted Magnetic Recording) or a similar thermally-assisted technology, (c) then DIscrete Track Media or Bit-Patterned Media or both?

Adding platter is the easiest but it also adds overall cost and if too many platters, drive thickness so this only gets you so far.  Shingle writing requires work on the servo system and track following (so firmware and electronic issues) but it requires no changes in the media and little if any on the heads.  However there are significant architectural and use case issues.

Write performance could suffer once the drive is fully written since a rewrite process would be required to add new data.  The memory management would get a bit like flash memory with their erase/write cycles. In addition to the performance hit the increase in TPI (tracks per inch) is probably only 30 per cent and at most 50 per cent and is a one time only bump.  As a consequence by 2014-2015 we will need some thing new such as HAMR or patterned media to continue the areal density growth.

These technologies still have significant technology or capital cost issues that get in the way of implementation so we may see a temporary decline in areal density growth to maybe 20 per cent for a couple of years.  Of course breakthroughs happen and like in semiconductor line width we could see paths to continued areal density increase that avoid a slow-down.

El Reg: What are the timescales and areal densities and capacities involved with each of these?

Unaided perpendicular recording gets us to about 1Tbit/in2, shingle writing gets us at best to 1.5Tbit/in2 (and by the way WORM type applications such as backup and DVRs may do fine with this approach).  If we are to achieve 2Tbit/in2 or higher we need some new breakthrough that is currently unclear or HAMR or patterned media.

El Reg: Will we see 12Gbit/s SAS interfaces? Will drives with additional platters need such a faster interface?

I think faster interfaces are quite likely.  In particular SSDs can already saturate 6Gbit/s interfaces today and could also do that tomorrow. Also these channels (or controllers) may be shared between devices and thus we need a higher composite data rate to support these devices than any one device would require.

El Reg: Will we see pure USB interfaces for external drives with no SATA interface at all and no need for a SATA-to-USB bridge inside the drive?

Maybe, we could see more specialisation in drives for external storage such as this, combined with shingled writing as well perhaps?  Also what about Light Peak?

Coughlin is seeing two intermediate technologies capable of boosting capacity before there is a transition to post-PMR Technologies. These are adding platters and heads on the one hand, and shingled writing on the other. My opinion is that we could see these in 2011 and 2012, These would be followed by either HAMR or patterned media. These I reckon are a post-2013 story.

It appears that the use of single platter drives and hybrid SSD-HDD products would enable HDD technology to withstand flash replacement of HDDs in some sectors of the HDD market. These will be a 2011 story, possibly a late-2010 one as Seagate's Momentus XT is out there already. ®

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