Why does an online change of the Ceph tunables "mon_osd_full_ratio" and "mon_osd_nearfull_ratio" does not take effect ?

Environment

• Red Hat Ceph Storage 1.2.3
• Red Hat Ceph Storage 1.2.3
• Ceph upstream firefly and Hammer

Issue

• Why does an online change of the Ceph tunables mon_osd_full_ratio and mon_osd_nearfull_ratio does not take effect ?

Resolution

• mon_osd_full_ratio and mon_osd_nearfull_ratio are not used for changing the values of nearfull_ratio and full_ratio for PGs (OSDs).

• In place of mon_osd_full_ratio and mon_osd_nearfull_ratio, please use ceph pg set_full_ratio and ceph pg set_nearfull_ratio commands.

 $ ceph pg  set_full_ratio <value> 
 $ ceph pg  set_nearfull_ratio <value>

Root Cause

• Both mon_osd_full_ratio and mon_osd_nearfull_ratio are used by Ceph to set the default values of filling ration and near-fill ratio, while creating placement groups.

• Instead of using these tunables, use ceph pg set_full_ratio <value> and ceph pg set_nearfull_ratio <value>.

Diagnostic Steps

$ ceph health detail
HEALTH_ERR 2 full osd(s); 140 near full osd(s)
osd.39 is full at 72%
osd.298 is full at 70%

$ ceph daemon /var/run/ceph/ceph-osd.39.asok config show | grep -i full_ratio
  "mon_osd_full_ratio": "0.95",
  "mon_osd_nearfull_ratio": "0.85",
  "osd_backfill_full_ratio": "0.85",
  "osd_pool_default_cache_target_full_ratio": "0.8",
  "osd_failsafe_full_ratio": "0.97",
  "osd_failsafe_nearfull_ratio": "0.9",

$ ceph daemon /var/run/ceph/ceph-osd.298.asok config show | grep -i full_ratio
  "mon_osd_full_ratio": "0.95",
  "mon_osd_nearfull_ratio": "0.85",
  "osd_backfill_full_ratio": "0.85",
  "osd_pool_default_cache_target_full_ratio": "0.8",
  "osd_failsafe_full_ratio": "0.97",
  "osd_failsafe_nearfull_ratio": "0.9",

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