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
