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vm:proxmox:ceph:pg [2023/07/03 20:28] – created niziakvm:proxmox:ceph:pg [2025/10/31 17:51] (current) – [reweight] niziak
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 PG PG
  
 +
 +===== Calculations =====
 +
 +  * [[https://old.ceph.com/pgcalc/]]
 +  * Max PG per OSD is 300
 +  * Result must be rounded up to the nearest power of 2.
 +
 +===== reweight =====
 +
 +Adjust reweight according to current OSD utilisation - to prevent filling one OSD
 +<code bash>ceph osd reweight-by-utilization</code>
 +
 +In CRUSH hierarchies with a smaller number of OSDs, it’s possible for some OSDs 
 +to get more PGs than other OSDs, resulting in a higher load. You can reweight 
 +OSDs by PG distribution to address this situation by executing the following:
 +
 +<code>
 +osd reweight-by-pg [<oload:int>] [<max_change:float>] [<max_osds:int>] [<pools>...]            reweight OSDs by PG distribution [overload-percentage-for-consideration, default 120]
 +</code>
 +
 +<code bash>ceph osd reweight-by-pg 101 0.05 999</code>
 +
 +NOTE: 
 +  * 101 is a ''oload'' parameter, which means ''overload percentage for consideration 101%''. For example, an argument of 200 would reweight OSDs which are twice as utilized as the average OSD.
 +  * 0.05 is a ''mach_change'' - maximum modification of weight
 +  * max_osds - maximum number of OSD to be modifies (default is 4)
 +
 +
 +
 +
 +
 +===== Balancer =====
 +
 +When the cluster is healthy, the balancer will incrementally move a small fraction of unbalanced PGs in order to improve distribution. This fraction will not exceed a certain threshold that defaults to 5%.
 +Set it to 1%:
 +<code bash>ceph config set mgr target_max_misplaced_ratio .01</code>