On Sun, 26 Mar 2006, Per Jessen wrote:
S Glasoe wrote:
Yeah, that seems to be a good option. Unfortunately the Storageworks controller does not support mirrors built on top of RAID5 sets,
Drop the parity on the RAID5 and you have a RAID10. What's the point of wasting the time calculating parity? You lose space with RAID5 mirrored to another RAID5 versus same number of drives in a RAID10. Same number of points of failure also. RAID10 baby!
But with a RAID15 (two mirrored RAID5s) I can survive a two-disk fsilure - one in each RAID5 or two in one RAID5. That doesn't quite work with a RAID10 array. It'll take any number of failures in any one stripe, but if two failures occur one in each stripe, I'm dead. Or am I missing something?
And that is what is nice about raid 55. Use the hardware (if you like)
to build 3 raid5's. Then use software to raid5 those. You can suffer
/all/ drives failing in one of the component raid5's *and* 1 drive in
the other hardware raid5. Or, you could make 12 raid 1's of two drives
each and build software raid 55 on top of that, or whatever.
--
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Carp in denim - There's a fish in my pants!
Jon Nelson