I found the other day even though I had 0 weighted OSDs, there was still weight 
in the containing buckets which triggered some rebalancing.

Maybe it is something similar, there was weight added to the bucket even though 
the OSD underneath was 0.


> -----Original Message-----
> From: ceph-users [mailto:[email protected]] On Behalf Of
> Christian Balzer
> Sent: Wednesday, 21 December 2016 12:39 PM
> To: [email protected]
> Subject: [ceph-users] When Zero isn't 0 (Crush weight mysteries)
>
>
> Hello,
>
> I just (manually) added 1 OSD each to my 2 cache-tier nodes.
> The plan was/is to actually do the data-migration at the least busiest day in
> Japan, New Years (the actual holiday is January 2nd this year).
>
> So I was going to have everything up and in but at weight 0 initially.
>
> Alas at the "ceph osd crush add osd.x0 0 host=ceph-0x" steps Ceph happily
> started to juggle a few PGs (about 7 total) around, despite of course no
> weight in the cluster changing at all.
> No harm done (this is the fast and not too busy cache-tier after all), but 
> very
> much unexpected.
>
> So which part of the CRUSH algorithm goes around and pulls weights out of
> thin air?
>
> Christian
> --
> Christian Balzer        Network/Systems Engineer
> [email protected]   Global OnLine Japan/Rakuten Communications
> http://www.gol.com/
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