Re: Hardware for PG

On Thu, 2002-07-11 at 18:37, Joshua D. Drake wrote:
> Hello,
>
>   Ahhh that is not true. RAID 5 is much, much faster than a mirror (RAID
> 1). I believe you are thinking about mirrored + striped which is RAID10
> (also know as 1+0). That is faster than RAID 5 but requires 4 disks
> where RAID 5 requires 3.

I'd be careful with such general statements. RAID5 may be much faster
than mirroring when reading, especially as the number of disks
increases. But with RAID5 writing is usually slower (a typical
one-stripe-size write requires at least 2 blocks to be read and written
again, hitting 2 disks 2 twice. Only n-1-stripe-size writes (where n = #
of disks in the array) can be done without reading first).

And, btw, RAID10 and RAID 1+0 is not necessarily the same. Depending on
the vendor, one is a striped set of mirrored disks, the other a mirrored
set of striped disks. RAID 0+1 is also sometimes used to mean the same
thing (one or the other).

cheers
-- vbi

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