On Sun, 2 May 2010, Richard Elling wrote:
These calculations are based on fixed MTBF. But disk MTBF decreases with
age. Most disks are only rated at 3-5 years of expected lifetime. Hence,
use solutions with longer lifetimes (high quality tape = 30 years) and plans for
migrating the data to newer media before the expected media lifetime is reached.
In short, if you don't expect to read your 5-year lifetime rated disk for
another 5 years,
then your solution is uhmm... shall we say... in need of improvement.
Yes, the hardware does not last forever. It only needs to last while
it is still being used and should only be used during its expected
service life. Your point is a good one.
On the flip-side, using 'zfs scrub' puts more stress on the system
which may make it more likely to fail. It increases load on the power
supplies, CPUs, interfaces, and disks. A system which might work fine
under normal load may be stressed and misbehave under scrub. Using
scrub on a weak system could actually increase the chance of data
ZFS storage and performance consulting at http://www.RichardElling.com
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