For due diligence I have to ask: are you running a recent Ceph release, not like Firefly? There were certain bugs back then...
On May 23, 2025, at 4:07 AM, Szabo, Istvan (Agoda) <Istvan.Szabo@agoda.com> wrote:
Hi,
For some reason this is the 2nd time I got into the same issue, added a new node at the time when in the cluster the most full osd was 73% and all the newly added osds now started to be between 70-80% full half way on the way to finish the rebalance.
Did they or their hosts somehow get the wrong CRUSH weight? `ceph osd df tree` and `ceph osd tree` would give us some insights.
I don't understand why, could this be because mgr upmap mode with deviation 1?
No, that’s reasonable especially if you have OSDs of multiple sizes.
Another question, I have 7 disks in each servers, however in the newly added one I still have 4 as spare which is not added. Just to get out of this space issue, would it cause any issue if I add the remaining 4 spare disk
I wouldn’t think so.
(which will cause unbalanced server size in the cluster, the weight of each server is 100TB, this would cause only this node to be 160TB).
Depending on your replication/EC profiles, CRUSH rules, and number of failure domains that extra capacity may or may not increase the cluster’s capacity, but for sure it should decrease the average fillage of the OSDs on that host, unless you’re adding them in such a way that skews the host’s CRUSH weight. Sometimes with a thundering herd of backfill OSDs can temporarily increase in fillage. When you add OSDs, it’s not entirely the case that only data “moving” to the new OSDs will be remapped, some existing data may be reshuffled as well, though this is much less than with old releases. Also, when backfilling Ceph will write new replicas before removing displaced replicas, in order to ensure safety. Usually this doesn’t result in quite the percentages you report, but upmap-remapped can help manage this dynamic.
Thank you
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