Hi Sage, Thanks for the answer, it has helped me a lot. Regards, Oleg On Wed, Aug 23, 2017 at 5:04 PM, Sage Weil <sage@xxxxxxxxxxxx> wrote: > On Tue, 22 Aug 2017, Oleg Kolosov wrote: >> Hi >> I'm working on a new erasure code, different than the one implemented >> in ceph lrc plugin. I'm trying to understand how ceph lrc plugin >> allocates shards in a layer, but it's not clear from the code. >> >> For example, say I have a local group containing shards 0,1,2,5 >> While 0,1,2 are data and 5 is parity. I'd like to place all of these >> shards in the same rack. >> >> Where in lrc .cc code these shards, which are composing a single >> layer, are allocated to the same rack? > > The EC code has to be carefully matched with a CRUSH rule that lays things > out properly. This is the reason that the EC crush rules are tied > to the erasure code profiles and the plugin handles rule creation. > > In the LRC case, you have a rule like > > take root > choose 3 rack > choose 5 osd > > to get a set of 15 shards, in groups of 5. The LRC plugin has some logic > to put the original data shards in the first 3 or 4 shards of each of > those sets of 5, and the parity blocks in the remaing slots. You'll want > to do something similar. Bonus points if you can reuse the scheme that > LRC uses... > > sage -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
