Re: RAID 5 vs RAID 10 benchmark

"Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> wrote in message news:<co7aa9$nfn$1_at_sparta.btinternet.com>...
>
> If you consider a single stripe across the traditional 5-disc raid, then
> either
> (a) the dead disk is the parity disk (one time in 5) - in which case
> reads
> don't do any extra reads, and you no longer have a write overhead
> on the other four.
> or
> (b) the dead disk is one of the data disks (4 chances in 5) - in which
> case
> three of the possibly reads won't have to do any extra reads, and
> only
> one read in 4 will have to read the other three disks and the parity
> disk
> to infer re-create the fourth set of data.
>

Shouldn't the parity disk have a higher risk of failing because it is pounded on more heavily than the others?

(Personally, I've seen two disks go out more than once, and haven't seen a parity disk go out alone, but I don't think what I've seen is representative. But I do think a batch of disks manufactured together will be more like each other than like those from another batch. And I've seen bad batches from IBM.)

jg

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