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SubjectRe: raid0 slower than devices it is assembled of?
Date
In article <Pine.LNX.4.58.0312170758220.8541@home.osdl.org>,
Linus Torvalds <torvalds@osdl.org> wrote:
|
|
| On Wed, 17 Dec 2003, Peter Zaitsev wrote:
| >
| > I'm pretty curious about this argument,
| >
| > Practically as RAID5 uses XOR for checksum computation you do not have
| > to read the whole stripe to recompute the checksum.
|
| Ahh, good point. Ignore my argument - large stripes should work well. Mea
| culpa, I forgot how simple the parity thing is, and that it is "local".
|
| However, since seeking will be limited by the checksum drive anyway (for
| writing), the advantages of large stripes in trying to keep the disks
| independent aren't as one-sided.

There is no "the" parity drive, remember the RAID-5 parity is
distributed. A write takes two seeks, a read, a data write, and a parity
write, but the parity isn't a bottleneck, and as noted above the size
only need be the blocks containing the modified data.
--
bill davidsen <davidsen@tmr.com>
CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.
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