On Wed, Nov 15, 2017 at 2:07 PM Bryan Henderson <[email protected]> wrote:
> Some questions about maps and epochs: > > I see that I can control the minimum number of osdmap epochs to keep with > "mon min osdmap epoch". Why do I care? Why would I want any but the > current > osdmap, and why would the system keep more than my minimum? > > Similarly, "mon max pgmap epoch" controls the _maximum_ number of pgmap > epochs > to keep around. I believe I need more than the most recent pgmap because I > need to keep previous ones until all PGs that were placed according to that > pgmap have migrated to where the current pgmap says they should be. But > do I > need more epochs than that, and what happens if the maximum I set is too > low > to cover those necessesary old pgmaps? > Ah, you're a bit backwards here. Despite, the name, the "pgmap" is a reporting structure about how much space PGs use, but it *does not* control where the PGs are placed. That's entirely determined by the OSDMap. So the cluster needs older OSDMaps to do peering and make sure it gets up-to-date PG data when doing replication/peering/recovery/etc. The PGMaps are only useful for reporting statistics. I don't think you as a user have any good reason to mess around with these at this point. -Greg > > -- > Bryan Henderson San Jose, California > _______________________________________________ > ceph-users mailing list > [email protected] > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >
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