RHEL to FreeBSD file server
Bob Friesenhahn
bfriesen at simple.dallas.tx.us
Tue Nov 13 17:41:17 UTC 2012
On Mon, 12 Nov 2012, kpneal at pobox.com wrote:
>
> With your setup of 11 mirrors you have a good mixture of read and write
> performance, but you've compromised on the safety. The reason that RAID 6
> (and thus raidz2) and up were invented was because drives that get used
> together tend to fail together. If you lose a drive in a mirror there is
> an elevated probability that the replacement drive will not be in place
> before the remaining leg of the mirror fails. If that happens then you've
> lost the pool. (Drive failures are _not_ independent.)
Do you have a reference to independent data which supports this claim
that drive failures are not independent? The whole function of RAID
assumes that drive failures are independent.
If drives share a chassis, care should be taken to make sure that
redundant drives are not in physical proximity to each other and that
they are supported via a different controller, I/O path, and power
supply. If the drives are in a different chassis then their failures
should be completely independent outside of a shared event like power
surge, fire, EMP, flood, or sun-spot activity.
The idea of raidz2 vdevs of four drives each sounds nice but will
suffer from decreased performance and increased time to replace a
failed disk. There are always tradeoffs.
Bob
--
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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