On 2012-01-24, at 5:23 PM, NeilBrown wrote: > On Thu, 19 Jan 2012 01:42:12 +0200 Boaz Harrosh <bharrosh@xxxxxxxxxxx> wrote: > >>>> Or possibly modify md-raid5 not to snapshot dirty pages prior to xor/write? >>>> (I never really bothered to find out if it really does this.) >> >> md-raid5/1 currently copies all pages if that what you meant. >> > > Small correction: RAID5 and RAID6 copy all pages. > RAID1 and RAID10 do not. > > If the incoming bios had nicely aligned pages which were somehow flagged to > say that they would not change until the request completed, then it should be > trivial to avoid that copy. Lustre has a patch to that effect that we've been carrying for several years. It avoids copying of the pages submitted to the RAID5/6 layer, and provides a significant improvement in performance and efficiency. A version of the patches for RHEL6 is available at: http://review.whamcloud.com/1142 though I don't know how close it is to working with the latest kernel. Cheers, Andreas -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
