On 09/04/2018 09:47 AM, Jörg Kastning wrote: > My questions are: > > 1. What does active+undersized actually mean? I did not find anything > about it in the documentation on docs.ceph.com.
http://docs.ceph.com/docs/master/rados/operations/pg-states/ active Ceph will process requests to the placement group. undersized The placement group has fewer copies than the configured pool replication level. Your crush map/rules and osds do not allow to have all pgs on three "independent" osds, so pgs have fewer copies than configured. > 2. Why are only 15 PGs were getting remapped after I've corrected the > mistake with the wrong pgp_num value? By pure chance 15 pgs are now actually replicated to all 3 osds, so they have enough copies (clean). But the placement is "wrong", it would like to move the data to different osds (remapped) if possible. It replicated to 2 osds in the initial placement but wasn't able to find a suitable third osd. Then by increasing pgp_num it recalculated the placement, again selected two osds and moved the data there. It won't remove the data from the "wrong" osd until it has a new place for it, so you end up with three copies, but remapped pgs. > 3. What's wrong here and what do I have to do to get the cluster back > to active+clean, again? I guess you want to have "two copies in dc1, one copy in dc2"? If you stay with only 3 osds that is the only way to distribute 3 objects anyway, so you don't need any crush rule. What your crush rule is currently expressing is "in the default root, select n buckets (where n is the pool size, 3 in this case) of type datacenter, select one leaf (meaning osd) in each datacenter". You only have 2 datacenter buckets, so that will only ever select 2 osds. If your cluster is going to grow to at least 2 osds in each dc, you can go with http://cephnotes.ksperis.com/blog/2017/01/23/crushmap-for-2-dc/ I would translate this crush rule as "in the default root, select 2 buckets of type datacenter, select n-1 (where n is the pool size, so here 3-1 = 2) leafs in each datacenter" You will need at least two osds in each dc for this, because it is random (with respect to the weights) in which dc the 2 copies will be placed and which gets the remaining copy. Best regards, Lothar -- Lothar Gesslein Linux Consultant Mail: gessl...@b1-systems.de B1 Systems GmbH Osterfeldstraße 7 / 85088 Vohburg / http://www.b1-systems.de GF: Ralph Dehner / Unternehmenssitz: Vohburg / AG: Ingolstadt,HRB 3537
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