> To be honest with 3:8 we could protect the cluster more from osd flapping. > Let's say you have less chance to have 8 down pgs on 8 separate nodes then with 8:3 only 3pgs on 3 nodes. > Of course this comes with the cost on storage used. > Is there any disadvantage performance wise on this? A few years back someone asserted that EC values with small prime factors are advantageous, so 23,11 would be doubleplus ungood. In general EC comes with a write tradeoff: each write (today) touches k+m hosts/OSDs, which means increased network amp and write IOPs amp. The latter can be painful for rotational OSDs. This additionally means that recovery/backfill are slower, as more OSDs are tied up with each op and thus fewer PGs can recover in parallel. >> I'm trying to understand what is the benefit of the higher coding chunks? You can use smaller object size? >> Let's say 4:2 the minimum object size should be 24K at least or with 8:3 it would be 44K because nothing will be stored on smaller space. >> In case of k=3 m=8, smallest object can be 12K, but you can lose 8 nodes (pgs) and data still there? BlueStore will allocate no less than min_alloc_size on a given OSD; the default is 4KB for most media. I think the above implies that parity shards don’t take space, but in fact an m shard uses space just like a k shard, so for space efficiency what matters is the sum of k+m, not their specific values. https://docs.google.com/spreadsheets/d/1rpGfScgG-GLoIGMJWDixEkqs-On9w8nAUToPQjN8bDI/edit?gid=358760253#gid=358760253; Bluestore Space Amplification Cheat Sheet docs.google.com >> >> Ty >> _______________________________________________ >> ceph-users mailing list -- ceph-users@xxxxxxx >> To unsubscribe send an email to ceph-users-leave@xxxxxxx > > > > -- > Alexander Patrakov > _______________________________________________ > ceph-users mailing list -- ceph-users@xxxxxxx > To unsubscribe send an email to ceph-users-leave@xxxxxxx _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
 |