William Hooper wrote:
You are right, in the apples and oranges. What I took out of it was the opinion that while most people are happy with RAID5, it's the poor cousin where multiple drive failures are concerned. Also, I get the impression (from my own experience) RAID5 tends to get pushed by salespeople because it is the cheapest RAID to implement.
Apples and oranges. If you are going to compare multiple sets, why not
compare 4 RAID5 sets w/ 3 disks each (12 in total).
I'm not sure how he figured this number. I do know that when I figured some numbers out for myself I used 3x4 rather than 2x4 like he did.
If you lose 5/12 RAID10s you still have over a 95% chance of no data lost. I believe recovery time on RAID10 puts RAID5 to shame too. His entire rant can be found at http://groups.google.com.au/groups?q=quarterly+raid+5+rant+group:comp.databases.informix&hl=en&lr=&ie=UTF-8&group=comp.databases.informix&selm=pan.2003.07.31.16.49.22.318281.15473%40bloomberg.net&rnum=5
He answers your question there: "Well with RAID10 there is no danger unless the one mirror that is recovering also fails and that's 80% or more less likely than that any other drive in a RAID5 array will fail!"
Unless my terminology is wrong, it's only one RAID10 set, that is, multiple RAID1 sets making up a RAID0 stripe. RAID1+0 as I think some people call it.
Of course, he falls into the same trap you did, comparing a single RAID5 set with multiple RAID10 sets.
However, you are right in that there is no reason you can't make it a RAID1+5 with 10 disks or even 15 disks to give the same sorts of protection or better than the 12 disk RAID10. I take the rant along the lines of "if you're going to the trouble, go with the best you can, and RAID5 isn't it". This is why I'm interested in why other's have RAID failures and what they plan(ned) to do next.
-- Scott Burns Mirrabooka Systems
Tel +61 7 3857 7899
Fax +61 7 3857 1368
