Bug 1907884

Summary: [DDF] The usable capacity is not so straight forward when Ceph comes into picture.
Product: [Red Hat Storage] Red Hat OpenShift Container Storage Reporter: Direct Docs Feedback <ddf-bot>
Component: documentationAssignee: Anjana Suparna Sriram <asriram>
Status: NEW --- QA Contact: Elad <ebenahar>
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Version: 4.5CC: asriram
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Description Direct Docs Feedback 2020-12-15 12:56:41 UTC 
The usable capacity is not so straight forward when Ceph comes into picture.

With Ceph we take into consideration the 'mon_osd_full_ratio' which is 85%, so we loose 15% usable space here. Also the usable capacity depends on the OSD with the lowest free disk size available.

The formula used to calculate MAX_AVAIL for pool is below:

min(osd.avail for osd in OSD_up)* len(osd.avail for osd in OSD_up) /pool.size() 

Reported by: rhn-support-assingh

https://access.redhat.com/documentation/en-us/red_hat_openshift_container_storage/4.5/html/planning_your_deployment/infrastructure-requirements_rhocs#annotations:cadcf3c1-3433-4285-a862-3596f5d448e1