On Thu, Jul 26, 2018 at 4:57 PM Benoit Hudzia <benoit@xxxxxxxxxxxxxxx> wrote:
HI,We currently segregate ceph pool PG allocation using the crush device class ruleset as described: https://ceph.com/community/new-luminous-crush-device-classes/simply using the following command to define the rule : ceph osd crush rule create-replicated <RULE> default host <DEVICE CLASS>However, we noticed that the rule is not strict in certain scenarios. By that, I mean that if there is no OSD of the specific device class ceph will allocate PG for this pool to any other OSD available ( creating an issue with the PG calculation when we want to add new pool)Simple scenario :1. create 1 Pool : <pool1> , replication 2 with 4 nodes , 1 OSD each . belonging to class <pool1>2. remove all OSD ( delete them )3. create 4 new OSD (using same disk but different ID) but this time tag them with class <pool2>4. Try to create pool <pool2> -> this will fail withthe pool creation will fail with output : Error ERANGE: pg_num 256 size 2 would mean 1024 total pgs, which exceeds max 800 (mon_max_pg_per_osd 200 * num_in_osds 4)"Pool1 simply started allocating PG to OSD that doesn't belong to the ruleset
Are you sure pool 1's PGs are actually being placed on the wrong OSDs? Have you looked at the output of "ceph pg dump" to check that?
It sounds more like the pool creation check is simply failing to consider the crush rules and applying a cruder global check.
John
_______________________________________________Which leads me to the following question: is there a way to make the crush rule a hard requirement. E.g : if we do not have any osd matching the device class , it won't start trying to allocate pg to OSD that doesn't match it?Is there any way to prevent pool 1 to use the OSD ?
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