On Feb 5, 2012, at 5:42 PM, Boris Epstein <borepstein@xxxxxxxxx> wrote:
> What you are saying seems to make sense actually. I wonder how much a RAID6
> with a few spares would make sense. If we are talking a large number of
> disks then RAID 6 + 2 spares means overpaying only for 5 disks. Not a lot
> if the total number of them is, say, 20.
Don't approach it as purely a cost analysis, but what you require for your application.
If you have a write-mostly transactional application then RAID10 makes sense, if you have 50/50 app then maybe a RAID50 out of several small RAID5s, if you have a read mostly or long-term archival storage then a RAID6.
I wouldn't create an array out of more then 12 disks unless it was a RAID10 cause rebuild times would put the array in jeopardy of a cascading failure. You could create a RAID50 out of 3 6 disk RAID5s with 2 hot spares. That's 15 disk usable space with 3 disks of parity and 2 disk spares. That would give decent performance with ability to handle 3 disk failures (spread across different RAID5s). When setting it up setup every third disk as part of a RAID5 just cause I have seen double failures and for some reason they were side-by-side for me.
It might be easier to do the striping in software cause that's a zero over-head operation and it makes the hardware RAID easier to setup, maintain and can make rebuilds less painful depending on the controller.
-Ross
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