On Thu, Dec 29, 2011 at 9:52 PM, Mikael Abrahamsson <swmike@xxxxxxxxx> wrote: > On Thu, 29 Dec 2011, Marcus Sorensen wrote: > >> My only suggestion would be to experiment with various partitioning, > > > Poster already said they're not partitioned. Correct. using partitioning allows you to adjust the alignment, so for example if the MD superblock at the front moves the start of the exported MD device out of alignment with the base disks, you could compensate for it by starting your partition on the correct offset. > >> On Thu, Dec 29, 2011 at 7:00 PM, Zdenek Kaspar <zkaspar82@xxxxxxxxx> >> wrote: >>> >>> Dne 30.12.2011 0:28, Michele Codutti napsal(a): >>>> >>>> The drives are not partitioned. I'm using the default chunk size (512K) >>>> and the default metadata superblock version (1.2). > > > My recommendation would be to look into the stripe-cache settings and check > iostat -x 5 output. What is most likely happening is that when writing to > the raid5, it's reading some (to calculate parity most likely) and not just > writing. iostat will confirm if this is indeed the case. > > Also, using raid5 for 2TB drives or larger is not recommended, use RAID6 > <http://www.zdnet.com/blog/storage/why-raid-5-stops-working-in-2009/162>. If he's writing full stripes he doesn't need to calculate parity by reading. I'm not sure how the MD layer determines this though, unless he's adding a sync or o_direct flag to his test he should be writing full stripes regardless of the blocksize he sets. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
