Hi Anthony and others,
I have now increased the number of PGs on my cluster, but the results are a bit
surprising:
I increased the settings by 4x and obtained a PG increase by 8x.
Wondering if you have insights why that might be.
Details:
Defaults:
mon_target_pg_per_osd 100
mon_max_pg_per_osd 250
`ceph osd pool autoscale-status` before:
POOL SIZE TARGET SIZE RATE RAW CAPACITY RATIO TARGET
RATIO EFFECTIVE RATIO BIAS PG_NUM NEW PG_NUM AUTOSCALE BULK
.mgr 435.8M 3.0 6788G 0.0002
1.0 1 on False
data 0 3.0 6788G 0.0000
1.0 1024 on False
data_ec 345.1T 1.5 876.4T 0.5906
1.0 256 on False
metadata 123.8G 3.0 6788G 0.0548
4.0 64 on False
I increased the `*_pg_per_osd` settings by 4x by running:
ceph config set global mon_target_pg_per_osd 400
ceph config set global mon_max_pg_per_osd 1000
`ceph osd pool autoscale-status` after:
# ceph osd pool autoscale-status
POOL SIZE TARGET SIZE RATE RAW CAPACITY RATIO TARGET
RATIO EFFECTIVE RATIO BIAS PG_NUM NEW PG_NUM AUTOSCALE BULK
.mgr 435.8M 3.0 6788G 0.0002
1.0 1 on False
data 0 3.0 6788G 0.0000
1.0 1024 on False
data_ec 345.1T 1.5 876.4T 0.5907
1.0 256 2048 on False
metadata 123.8G 3.0 6788G 0.0548
4.0 64 512 on False
`ceph osd pool autoscale-status` after a few minutes more:
# ceph osd pool autoscale-status
POOL SIZE TARGET SIZE RATE RAW CAPACITY RATIO TARGET
RATIO EFFECTIVE RATIO BIAS PG_NUM NEW PG_NUM AUTOSCALE BULK
.mgr 435.8M 3.0 6788G 0.0002
1.0 1 on False
data 0 3.0 6788G 0.0000
1.0 1024 on False
data_ec 343.9T 1.5 876.4T 0.5886
1.0 2048 on False
metadata 127.5G 3.0 6788G 0.0564
4.0 512 on False
So the `PG_NUM` for `data_ec` increased **8x**, from `256` to `2048`.
This is surprising to me:
* The Ceph autoscaler should increase `PG_NUM` by factors of 2x. It chose to not do that
in the "before" state.
* When I increased `*_pg_per_osd` settings by 4x, I consequently expected that
`PG_NUM` would increase by <= 4x. But it increased 8x.
Side remark:
While `PG_NUM` is already 2048, the actual number of PGs in `ceph status` is
still increasing (currently `1830 pgs`, and some being added every couple
minutes). I believe this part is as expected.
Thanks!
Niklas
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