Quoting Nick Fisk (n...@fisk.me.uk):
> Hi All,
> 
> Has anyone been testing the bluestore pool compression option?
> 
> I have set compression=snappy on a RBD pool. When I add a new bluestore OSD,
> data is not being compressed when backfilling, confirmed by looking at the
> perf dump results. If I then set again the compression type on the pool to
> snappy, then immediately data starts getting compressed. It seems like when
> a new OSD joins the cluster, it doesn't pick up the existing compression
> setting on the pool.
> 
> Anyone seeing anything similar? I will raise a bug if anyone can confirm.

Yes. I tried to reproduce your issue and I'm seeing the same thing. The
things I did to reproduce:

- check for compressed objects beforehand on osd (no compressed objects
  where there)

- remove one of the osds in the cluster

- ceph osd pool set CEPH-TEST-ONE compression_algorithm snappy
- ceph osd pool set CEPH-TEST-ONE compression_mode force
-  rbd clone a rbd image
- let cluster heal again
- check for compressed bluestore objects on "new" osd (ceph daemon osd.0 perf
dump | grep blue): 

"bluestore_compressed": 0,
"bluestore_compressed_allocated": 0,
"bluestore_compressed_original": 0

- check for compressed bluestore objects on already existing osd (ceph daemon
osd.1 perf dump | grep blue):

"bluestore_compressed": 2991873,
"bluestore_compressed_allocated": 3637248,
"bluestore_compressed_original": 10895360,

Gr. Stefan

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