SSDs start edging out spinning drives for storage

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.