On Tue, Feb 16 at 9:44, Brian E. Imhoff wrote:
But, at the end of the day, this is quite a bomb: "A single raidz2
vdev has about as many IOs per second as a single disk, which could
really hurt iSCSI performance."
If I have to break 24 disks up in to multiple vdevs to get the
expected performance might be a deal breaker. To keep raidz2
redundancy, I would have to lose..almost half of the available
storage to get reasonable IO speeds.
ZFS is quite flexible. You can put multiple vdevs in a pool, and dial
your performance/redundancy just about wherever you want them.
24 disks could be:
12x mirrored vdevs (best random IO, 50% capacity, any 1 failure absorbed, up to
12 w/ limits)
6x 4-disk raidz vdevs (75% capacity, any 1 failure absorbed, up to 6 with
limits)
4x 6-disk raidz vdevs (~83% capacity, any 1 failure absorbed, up to 4 with
limits)
4x 6-disk raidz2 vdevs (~66% capacity, any 2 failures absorbed, up to 8 with
limits)
1x 24-disk raidz2 vdev (~92% capacity, any 2 failures absorbed, worst random IO
perf)
etc.
I think the 4x 6-disk raidz2 vdev setup is quite commonly used with 24
disks available, but each application is different. We use mirrors
vdevs at work, with a separate box as a "live" backup using raidz of
larger SATA drives.
--eric
--
Eric D. Mudama
edmud...@mail.bounceswoosh.org
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