On Dec 25, 2009, at 6:01 PM, Jeroen Roodhart <j.r.roodh...@uva.nl>
wrote:
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Hi Freddie, list,
Option 4 is to re-do your pool, using fewer disks per raidz2 vdev,
giving more vdevs to the pool, and thus increasing the IOps for the
whole pool.
14 disks in a single raidz2 vdev is going to give horrible IO,
regardless of how fast the individual disks are.
Redoing it with 6-disk raidz2 vdevs, or even 8-drive raidz2 vdevs
will give you much better throughput.
We are aware of the configuration being possibly suboptimal. However,
before we had the SSDs, we did test earlier with 6x7 Z2 and even 2way
mirrorset setups. These gave better IOPS but not significantly enough
improvement (I would expect roughly a bit more than double the
performance in 14x3 vs 6x7) . In the end it is indeed a choice
between performance, space and security. Our hope is that the SSD
slogs "serialise" the data flow enough to make this work. But you
have a fair point and we will also look into the combination of SSDs
and pool-configurations.
Also, possibly the Vortex Turbo SSDs aren't as good latency wise as I
expected. Maybe the Sun SSDs will do a lot better. We will find this
out when they arrive (due somewhere in february).
Understand too that every write is striped across the vdev which means
the vdev has the IOPS of a single drive.
A 14 drive pool of mirrors would provide 7 times the IOPS then a 14
drive raidz2/3
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