Academic paper suggests flash may be better than disk for archiving data
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November 12, 2014
An academic paper suggests that flash could potentially be better than traditional disk
for data archiving.
The SSRC paper ''An Economic Perspective of Disk vs. Flash Media in Archival Storage'' was published
earlier this year, at the 22nd IEEE International Symposium on Modelling, Analysis, and Simulation of
Computer and Telecommunication Systems (MASCOTS 2014).
In it, lead author Preeti Gupta and her colleagues found that "archives based upon alternative
media (such as flash) are surprisingly cost competitive when compared with archives based upon traditional
disk media over the long-term".
They developed specialized algorithms to test the various costs of archival storage over a
period of years using disk and flash.
The paper starts off by saying that archiving software often resulted in storing data with
infrequent access, making tape a good fit even though it has a long access latency.
Recently though, data mining of archives has developed, which requires faster access and so
making disk preferential over tape.
Gupta and her colleagues looked at whether flash was as good as disk, or even better in this
low latency archive situation.
Long-term storage costs include media replacement for worn-out drives, and the industry expects
replacement disk products to have a higher capacity than the replaced drives, and with a lower per-GB
A main influence on replacement disk costs is the Kryder rate, "the annual proportional change in
bit density and thus a decrease in per-byte cost (so a rate at 0.2 means next year’s per-byte cost
would be 80 about percent of this year’s per-byte cost.
In fact, to make it clearer, "per-byte storage costs decrease as bit density increases at the Kryder
rate (annual storage density growth rate)."
The Kryder rate is slowing due to the dramatic increase in industry costs needed for a jump
to the next recording technology, HAMR (Heat-Assisted Magnetic Recording).
"Compared with pre-2010 projections, Figure 1 reveals that per-byte disk cost is now seven times
more expensive, and in six years would be around 200 times more expensive."
The researchers write: "The transitions to the next disk recording technology (HAMR) and its
probable successor (Bit-Patterned Media) could potentially turn out to be vastly more difficult
and expensive than expected, delaying further bit density improvements and thus decreasing the
The archival access pattern is described as write once, read rarely, overwrite rarely. Flash is
more expensive per-GB to buy than disk but costs less to use, also needing less power, space and cooling.
But as its geometry scales down, its endurance worsens, and that could present a problem. Flash
drive controllers, currently mostly optimized for performance, can also be optimized for endurance
instead and solve that issue.
The researcher also suggest that flash drives could be made with stronger insulation between
cells, at little extra cost, to increase the data retention period.
Source: The SSRC.
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