On 05/05/11 18:36, Florian Weimer wrote:
* Greg Smith:
Intel claims their Annual Failure Rate (AFR) on their SSDs in IT
deployments (not OEM ones) is 0.6%. Typical measured AFR rates for
mechanical drives is around 2% during their first year, spiking to 5%
afterwards. I suspect that Intel's numbers are actually much better
than the other manufacturers here, so a SSD from anyone else can
easily be less reliable than a regular hard drive still.
I'm a bit concerned with usage-dependent failures. Presumably, two SDDs
in a RAID-1 configuration are weared down in the same way, and it would
be rather inconvenient if they failed at the same point. With hard
disks, this doesn't seem to happen; even bad batches fail pretty much
randomly.
Actually I think it'll be the same as with hard disks.
ie. A batch of drives with sequential serial numbers will have a fairly
similar average lifetime, but they won't pop their clogs all on the same
day. (Unless there is an outside influence - see note 1)
The wearing-out of SSDs is not as exact as people seem to think. If the
drive is rated for 10,000 erase cycles, then that is meant to be a
MINIMUM amount. So most blocks will get more than that amount, and maybe
a small number will die before that amount. I guess it's a probability
curve, engineered such that 95% or some other high percentage will
outlast that count. (and the SSDs have reserved blocks which are
introduced to take over from failing blocks, invisibly to the end-user
-since it can always read from the failing-to-erase block)
Note 1:
I have seen an array that was powered on continuously for about six
years, which killed half the disks when it was finally powered down,
left to cool for a few hours, then started up again.
--
Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-general
