On 04/ 9/10 10:48 AM, Erik Trimble wrote:
Well....
The problem is (and this isn't just a ZFS issue) that resilver and scrub
times /are/ very bad for>1TB disks. This goes directly to the problem
of redundancy - if you don't really care about resilver/scrub issues,
then you really shouldn't bother to use Raidz or mirroring. It's pretty
much in the same ballpark.
That is,>1TB 3.5" drives have such long resilver/scrub times that with
ZFS, it's a good bet you can kill a second (or third) drive before you
can scrub or resilver in time to compensate for the already-failed one.
Put it another way, you get more errors before you have time to fix the
old ones, which effectively means you now can't fix errors before they
become permanent. Permanent errors = data loss.
That's one of the big problems with the build it now, expand with bigger
drives later approach. If you were designing from scratch with 2TB
drives, you would be wise to consider triple parity raid, where double
parity has acceptable reliability for 1TB drives. Each time drive
capacity double (and performance does not) an extra level or parity is
required. I guess this extrapolates to one data and N parity drives..
--
Ian.
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