❓ What?
The maximum / threshold percentage of disk space usage before an OSD is considered full. This happens after usage has crossed and Nearfull Ratio. The default value is 0.95 or 95% of the total available space / capacity.
❔ Why?
When a ceph cluster approaches full ratio, it sacrifices high availability: the cluster goes read-only at this ratio. All writes that are halted will result in degraded objects (objects that have less than Pool Size (size) ideal copies). Furthermore if the cluster has min_size 1 then it results in data loss. Therefore it’s not a good production practice.
🎤 How?
Full Ratio is set during cluster creation on the OSDMap as follows:
[global]
[...]
mon_osd_full_ratio = 0.95Afterwards, it can be changed with:
ceph osd set-full-ratioIn croit, Full Ratio can be changed by visiting Maintenance → Full Ratios (at the bottom):
👓 References
https://docs.ceph.com/en/quincy/rados/configuration/mon-config-ref/#storage-capacity