How many failure domains do you have? The downweighted hosts, are they spread across failure domains?
On Aug 18, 2025, at 10:28 AM, Justin Mammarella <justin.mammarella@unimelb.edu.au> wrote:
Hello,
We’re seeing the MAX_AVAIL value in ceph df instantaneously drop to 0 Bytes / 100% full when specific osds have their crush weight set to low values.
The osds are otherwise healthy, and ceph osd df does not show their utilization to be above 70%.
ceph version 19.2.2
CLASS SIZE AVAIL USED RAW USED %RAW USED mf1hdd 19 PiB 8.9 PiB 10 PiB 10 PiB 53.83
to
POOL ID PGS STORED OBJECTS USED %USED MAX AVAIL mf1fs_data 1 16384 6.8 PiB 2.51G 10 PiB 100.00 0 B
We’re running a 9+3 EC pool.
This cluster has 1139 osds / 46 host.
We’re in the process of downsizing the cluster and draining nodes via crush reweight is part of our normal operations.
It happened once a few weeks ago, and we isolated the issue to the weight on a single osd. Now it’s happening during rebalance on multiple osds, at some point the movement of PGs triggers an edge case causing the MAX AVAIL calculation to fail if the crush weight is too low.
Example crush weights
1418 mf1hdd 0.02000 osd.1418 up 1.00000 1.00000
1419 mf1hdd 0.02000 osd.1419 up 0 1.00000
2110 mf1hdd 0.02000 osd.2110 up 1.00000 1.00000
2111 mf1hdd 0.02000 osd.2111 up 0 1.00000
2112 nvmemeta 0.02000 osd.2112 up 1.00000 1.00000
Any ideas before I file a bug report?
Thankyou _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io