On Feb 5, 2010, at 10:49 AM, Robert Milkowski <mi...@task.gda.pl> wrote:
Actually, there is.
One difference is that when writing to a raid-z{1|2} pool compared
to raid-10 pool you should get better throughput if at least 4
drives are used. Basically it is due to the fact that in RAID-10 the
maximum you can get in terms of write throughput is a total
aggregated throughput of half the number of used disks and only
assuming there are no other bottlenecks between the OS and disks
especially as you need to take into account that you are double the
bandwidth requirements due to mirroring. In case of RAID-Zn you have
some extra overhead for writing additional checksum but other than
that you should get a write throughput closer to of T-N (where N is
a RAID-Z level) instead of T/2 in RAID-10.
That hasn't been my experience with raidz. I get a max read and write
IOPS of the slowest drive in the vdev.
Which makes sense because each write spans all drives and each read
spans all drives (except the parity drives) so they end up having the
performance characteristics of a single drive.
Now if you have enough drives you can create multiple raidz vdevs to
get the IOPS up, but you need a lot more drives then what multiple
mirror vdevs can provide IOPS wise with the same amount of spindles.
-Ross
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