Michael Stone writes:
I still don't follow that. Why would the RAID level matter? IOW, are you
actually wanting 2 spares, or are you just stick with that because you
need a factor of two disks for your mirrors?
RAID 10 needs pairs.. so we can either have no spares or 2 spares.
Mmm, it's a bit more complicated than that. RAID 10 can be better if you
have lots of random writes (though a large RAID cache can mitigate
that).
We are using a 3ware 9550SX with 128MB RAM (at least I believe that is what
that card has installed).
For small random reads the limiting factor is how
fast you can seek, and that number is based more on the number of disks than the RAID
level.
I don't have any solid stats, but I would guess the machines will fairly
close split between reads and writes.
hardware. The reason that RAID 10 can give better random small block
write performance is that fewer disks need to be involved per write.
That makes sense.
That's something that can be mitigated with a large cache
128MB enough in your opinion?
the writes, but some controllers are much better than others in that
regard.
The controller we are using is 3Ware 9550SX.
This is really a case where you have to test with your
particular hardware & data
That is obviously the ideal way to go, but it is very time consuming. :-(
To setup a machine with one set of raid setup.. test, then re-do with
different set of raid.. re test.. that's anywhere from 1 to 2 days worth of
testing. Unlikely I will be given that time to test.
