SSDs start edging out spinning drives for storage

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Written By: Peter Williams
Published: 27th May, 2009
Content Copyright © 2009 Bloor. All Rights Reserved.

Solid state disks (SSDs) are this year appearing within every vendor's equipment portfolio. Unlike spinning hard disk drives (HDDs) they do not revolve but, pardon the pun, this is the start of a disk revolution which will bring the demise of HDDs - although not quite yet.

Last week SNIA Europe's annual Academy event breezed into London. A full day of education on everything to do with data storage and networking, it is a good indicator of what's on the minds of those in the know among the data protection vendors. Storage virtualisation was a big theme as was the coming fibre channel over Ethernet (FCoE) standard. There were, too, a couple of items on SSDs.

I can remember a time when solid state disk (SSD) referred to a sealed disk unit incorporating a fixed ‘arm' with lots of read-write heads—making access much faster because there was no latency through head movement. We've come along way since then but drive head movement is still a major factor in performance.

Now SSD refers essentially to a memory stick designed in an HDD form factor with access virtualised so it behaves like an HDD. SSDs are screamingly fast for read-intensive applications (nanoseconds versus milliseconds for HDD) but writing can still be slow. Reliability is the equal or better of HDDs supporting a much wider temperature tolerance.

Write speed limitations are being addressed in some cases by a cached flash mix of non-volatile storage (slow for writing) and DDR RAM NAND flash (very fast but volatile so needing battery support even when idle).

So it is an SSD's capital cost (or price per GB) that is currently holding it back most, with the cached flash mix more expensive; but this will change. The technology was and is being developed for high volume sales consumer devices such as digital cameras. It is the high volume that will ensure commodity pricing will come—and when low enough, nobody will have a good reason to buy new HDDs.

Looking at the lifetime cost of SSDs already makes for a much better picture. SSDs have very low (in some cases negligible) power and cooling needs and a much lower footprint per GB of capacity; in laptops and PDAs, SSDs can yield major battery life extensions. So there really is no hiding place for HDDs going forward.

Speaking on SSDs at the SNIA event, Nick Baker of Sun Microsystems said: "The price per GB cross-over point could be 2013 but the IOPS [input-output per second] cross-over is now."

He added that SSD was happy about random I-O and good for video on demand, as well as "red hot for OLTP" (especially using DDR RAM versions).

At the same time HDD spin speeds and capacities are hitting a wall. The highest performance HDDs have stayed at 15,000 rpm for some time; at 20,000 rpm, Baker pointed out, the outer edge is travelling faster than the speed of sound.

SSD technology still has some challenges ahead—but HDDs must soon be on their way out.

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