On Sun, 01 May 2011 17:24:09 +0200 David Brown <david.brown@xxxxxxxxxxxx> wrote: > On 01/05/11 00:27, NeilBrown wrote: > > On Sat, 30 Apr 2011 16:27:48 +0100 pg_xf2@xxxxxxxxxxxxxxxxxx (Peter Grandi) > > wrote: > > > >> * Can Linux MD do "abbreviated" read-modify-write RAID6 > >> updates like for RAID5? That is where not the whole stripe > >> is read in, modified and written, but just the block to be > >> updated and the parity wblocks. > > > > No. (patches welcome). > > As far as I understand the raid6 mathematics, it shouldn't be too hard > to do such abbreviated updates, but that it could quickly lead to > complex code if you are trying to update more than a couple of blocks at > a time. The RAID5 code already handle some of this complexity. It would be quite easy to modify the code so that we have - list of 'old' data blocks - P and Q blocks - list of 'new' data blocks. We then just need to (optimised) maths to deduce the new P and Q given all of that. Of course you would only bother with a 7-or-more disk array.. NeilBrown -- 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
