[CentOS] Re: question about software Raid 1

Sun Sep 21 19:53:38 UTC 2008
John R Pierce <pierce at hogranch.com>

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 ...