On Mon, Nov 2, 2015 at 7:42 AM, Loris Cuoghi <lc@xxxxxxxxxxxxxxxxx> wrote: > Thanks Greg :) > > For the OSDs, I understand, on the other hand for intermediate abstractions > like hosts, racks and rooms, do you agree that it should currently be > possible to change the IDs (always under the "one change at a time, I > promise mom" rule)? Yeah, that should be fine. Actually changing a bunch of IDs shouldn't matter, but I haven't played with actually changing them so no promises. > > Clearly, a good amount of shuffling should be expected as a consequence. > Basically I was inquiring whether changing the id of a single host would > shuffle the entirety (or a relatively big chunk) of the cluster data, or if > the shuffling was limited to a direct proportion of the item's weight. > > I just --test-ed with crushtool. I changed an host's id, and testing the two > maps with : > > crushtool -i crush.map --test --show-statistics --rule 0 --num-rep 3 --min-x > 1 --max-x $N --show-mappings > > (with $N varying from as little as 32 to "big numbers"TM) shows that nearly > the 50% of the mappings changed, in a 10 hosts cluster. > > Thanks All :) > > > Le 02/11/2015 16:14, Gregory Farnum a écrit : >> >> Regardless of what the crush tool does, I wouldn't muck around with the >> IDs of the OSDs. The rest of Celh will probably not handle it well if >> the crush IDs don't match the OSD numbers. >> -Greg >> >> On Monday, November 2, 2015, Loris Cuoghi <lc@xxxxxxxxxxxxxxxxx >> <mailto:lc@xxxxxxxxxxxxxxxxx>> wrote: >> >> Le 02/11/2015 12:47, Wido den Hollander a écrit : >> >> >> >> On 02-11-15 12:30, Loris Cuoghi wrote: >> >> Hi All, >> >> We're currently on version 0.94.5 with three monitors and 75 >> OSDs. >> >> I've peeked at the decompiled CRUSH map, and I see that all >> ids are >> commented with '# Here be dragons!', or more literally : '# >> do not >> change unnecessarily'. >> >> Now, what would happen if an incautious user would happen to >> put his >> chubby fingers on this ids, totally disregarding the warning >> at the >> entrance of the cave, and change one of them? >> >> Data shuffle? (Relative to the allocation of PGs for the >> OSD/host/other >> item?) >> >> A *big* data shuffle? (ALL data would need to have its >> position >> recalculated, with immediate end-of-the-world data shuffle?) >> >> Nothing at all? (And the big fat warning is there only to >> take fun on >> the uninstructed ones? Not plausible...) >> >> >> Give it a try! Download the CRUSHMap and run tests on it with >> crushtool: >> >> $ crushtool -i mycrushmap --test --rule 0 --num-rep 3 >> --show-statistics >> >> Now, change the map, compile it and run again: >> >> $ crushtool -i mycrushmap.new --test --rule 0 --num-rep 3 >> --show-statistics >> >> Check the differences and you get the idea of how much has >> changed. >> >> Wido >> >> >> Thanks Wido ! :) >> >> Thanks ! >> >> Loris >> _______________________________________________ >> ceph-users mailing list >> ceph-users@xxxxxxxxxxxxxx >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >> >> _______________________________________________ >> ceph-users mailing list >> ceph-users@xxxxxxxxxxxxxx >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >> >> _______________________________________________ >> ceph-users mailing list >> ceph-users@xxxxxxxxxxxxxx >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >> > _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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