On Sun, 2008-09-21 at 12:53 -0700, John R Pierce wrote:
> Kay Diederichs wrote:
> > BTW, there is - even with current kernels - no speed gain in using
> > RAID1 - see http://kernelnewbies.org/KernelProjects/Raid1ReadBalancing .
>
> except, thats wrong. I unwrapped a recent kernel source tarball from
> kernel.org and found...
>
> static struct mirror *choose_mirror(struct mirror_set *ms, sector_t sector)
> {
> struct mirror *m = get_default_mirror(ms);
>
> do {
> if (likely(!atomic_read(&m->error_count)))
> return m;
>
> if (m-- == ms->mirror)
> m += ms->nr_mirrors;
> } while (m != get_default_mirror(ms));
>
> return NULL;
> }
>
>
> so it appears its a round robin ...
> _______________________________________________
This makes sense. I'm pretty sure that tests that I've run in the past
using bonnie++ or iozone showed faster reads with raid1 than with a
single drive. I would think that if the drives are on seperate
controllers (and depending upon the performance/capacity of the drives
and controllers), there could be notable improvements.
Nataraj
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