Thanks.
For replica, what is the best way to change crush profile ? Is it to
create a new replica profile, and set this profile as crush rulest for
the pool (something like ceph osd pool set {pool-name} crush_ruleset
my_new_rule) ?
For erasure coding, I would thus have to change the profile at least to
k=3, m=3 (for now I only have 6 osd servers).
But if I am correct, this cannot be changed for an existing pool and I
will have to create a new pool and migrate all data from the current one
to the new one. Is that correct ?
F.
Le 28/11/2019 à 17:51, Paul Emmerich a écrit :
Use a crush rule likes this for replica:
1) root default class XXX
2) choose 2 rooms
3) choose 2 disks
That'll get you 4 OSDs in two rooms and the first 3 of these get data,
the fourth will be ignored. That guarantees that losing a room will
lose you at most 2 out of 3 copies. This is for disaster recovery
only, it'll guarantee durability if you lose a room but not
availability.
3+2 erasure coding cannot be split across two rooms in this way
because, well, you need 3 out of 5 shards to survive, so you cannot
lose half of them.
Paul
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