Christian Pernegger wrote:
Not surprising at all. Read performance is similar between the two
setups as expected (appears to be limited by the PCI bus).
Yes, reads are fine.
Streaming write performance is better because you are writing less
redundant data to disks, you can now stripe writes over 5 disks
instead of 3.
Sounds reasonable. Write performance SHOULD be ~5x single disk for
raid5 and ~3x single disk for raid10 in a theoretical best-case
scenario, either should hit the PCI bus cap. In reality the ratios are
more like 1x for raid5 and 0.6 -1.1x for raid10. It's just that I'd
expected ~ identical and significantly better streaming write
performance from both array configurations ... then again, if you
think it over,
raid5 will transfer 1 parity block per 5 data blocks (so 5/6 of the
PCI bw are usable = 92MB)
raid10 will transfer 3 copy blocks per 3 data blocks (so 1/2 of the
PCI bw are usable = 55MB)
Factoring in some contention / overhead my values might well be
normal. It just means that the fabled raid10 only performs if you have
high-bw buses, which this box sadly doesn't, or a hw controller where
redundant blocks don't go over the bus, which the 3ware 7506
apparently isn't.
I'll still go with raid10 for the 50% better random I/O, only less
enthusiastically.
I think that you should treat 10,n2 and 10,f2 as separate
configurations, and test them as such. behavior is quite different, and
one or the other might be a better fit to your usage.
The ability to transfer a single copy of the data and no parity
information is an advantage of hardware controllers.
--
Bill Davidsen <davidsen@xxxxxxx>
"Woe unto the statesman who makes war without a reason that will still
be valid when the war is over..." Otto von Bismark
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