On Tue Dec 08, 2009 at 09:49:48PM +0800, hank peng wrote:
> 2009/12/8 Robin Hill <robin@xxxxxxxxxxxxxxx>:
> > On Tue Dec 08, 2009 at 09:01:23PM +0800, hank peng wrote:
> >
> >> Hi, all:
> >> As we know, when a raid5 array is created, recovery will be going on
> >> which involves some read, one xor and one write. Since there is no
> >> real data in the disk at the time, besides, if I am willing to wait
> >> for recovery to complete and then use this raid5, how about adding
> >> support for a fast recovery method? Right now, what is in my mind is
> >> zero all disks which belong to this raid5. I think it will increase
> >> raid5 recovery speed when created and decrease CPU usage, since all
> >> zero is also XORed.
> >> What do raid developers think?
> >>
> > It'll decrease CPU usage but increase I/O - you're now needing to write
> > to all disks. Most systems will be I/O limited rather than CPU limited,
> > so the current approach works better. If you want to zero the disks
> > then do this before creating the array - you can then use --assume-clean
> > to skip the resync process.
> >
> I think --assume-clean is used mostly when doing performance test and
> can't be used when creating a raid5 array using new disk, because
> later read and write operation make assumption that all stripe is
> XORed. Correct me if I am wrong.
>
You're correct - that's why I said to zero all the disks first so the
XOR data is all correct.
Cheers,
Robin
--
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( ' } | Robin Hill <robin@xxxxxxxxxxxxxxx> |
/ / ) | Little Jim says .... |
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