On Oct 24, 2006, at 12:33 PM, Frank Cusack wrote:
On October 24, 2006 9:19:07 AM -0700 "Anton B. Rang"
<[EMAIL PROTECTED]> wrote:
Our thinking is that if you want more redundancy than RAID-Z, you
should
use RAID-Z with double parity, which provides more reliability
and more
usable storage than a mirror of RAID-Zs would.
This is only true if the drives have either independent or identical
failure modes, I think. Consider two boxes, each containing ten
drives.
Creating RAID-Z within each box protects against single-drive
failures.
Mirroring the boxes together protects against single-box failures.
But mirroring also protects against single-drive failures.
Right, but mirrored raidz would in this case protect the admin from:
1) one entire jbod chassis/comm failure, and
2) individual drive failure in the remaining chassis during an
occurrence of (1)
Since the person is dealing with JBODS and not hardware RAID arrays,
my suggestion is to combine ZFS and SVM.
1) Use ZFS and make a raidz-based ZVOL of disks on each of the two JBODs
2) Use SVM to mirror the two ZVOLs. Newfs that with UFS.
Not at all optimal, but it'll work. It would be nice if you could
manage a mirror of existing vdevs within ZFS and this mirroring would
be a special case where it would be dumb and just present the volume
and pass through most of the stuff to the raidz (or whatever) vdev
below. It would be silly to double-cksum and compress everything, not
to mention the possibility of differing record sizes.
/dale
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