risner wrote:
> 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.
Yes.
> 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.)
>From what I can tell, this is purely a function of needed IOPS. Wider stripe
>= better storage/bandwidth utilization = less IOPS. For home usage I run a 14
>drive RAIDZ3 array.
> As for whether or not to do raidz, for me the
> issue is performance. I can't handle the raidz
> write penalty.
If there is a RAIDZ write penalty over mirroring, I am unaware of it. In fact,
sequential writes are faster under RAIDZ.
> If I needed triple drive protection,
> a 3way mirror setup would be the only way I would
> go.
That will give high IOPS with 33% storage utilization and 33% bandwidth
utilization. In other words, for every MB of data read/witten by an
application, 3MB is read/written from/to the array and stored.
Multiply all storage and bandwidth needs by three.
> I don't yet quite understand why a 3+ drive
> raidz2 vdev is better than a 3 drive mirror vdev?
> Other than a 5 drive setup is 3 drives of space
> when a 6 drive setup using 3 way mirror is only 2
> drive space.
Part of the question you answered yourself. The other part is that with a 6
drive RAIDZ3, I can lose ANY three drives and still be running. With three
mirrors, I can lose the pool if the wrong two drives die.
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