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.