ttabbal:
If I understand correctly, raidz{1} is 1 drive protection and space is
(drives - 1) available. Raidz2 is 2 drive protection and space is (drives - 2)
etc. Same for raidz3 being 3 drive protection.
Everything I've seen you should stay around 6-9 drives for raidz, so don't
do a raidz3 with 12 drives. Instead make two raidz3 with 6 drives each (which
is (6-3)*1.5 * 2 = 9 TB array.)
As for whether or not to do raidz, for me the issue is performance. I
can't handle the raidz write penalty. If I needed triple drive protection, a
3way mirror setup would be the only way I would go. I don't yet quite
understand why a 4+ drive raidz3 vdev is better than a 3 drive mirror vdev?
Other than a 6 drive setup is 3 drives of space when a 6 drive setup using 3
way mirror is only 2 drive space.
Adam Leventhal:
If we can compare apples and oranges, would you same recommendation ("use
raidz2 and/or raidz3") be the same when comparing to mirror with the same
number of drives? In other words, a 2 drive mirror compares to raidz{1} the
same as a 3 drive mirror compares to raidz2 and a 4 drive mirror compares to
raidz3? If you were enterprise (in other words card about perf) why would you
ever use raidz instead of throwing more drives at the problem and doing
mirroring with identical parity?
Joerg Moellenkamp:
I do "consider RAID5 as 'Stripeset with an interleaved Parity'", so I
don't agree with the strong objection in this thread by many about the use of
RAID5 to describe what raidz does. I don't think many particularly care about
the nuanced differences between hardware card RAID5 and raidz, other than
knowing they would rather have raidz over RAID5.
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