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