I seem to have a problem getting bluestore compression to do anything. I
followed the documentation and enabled bluestore compression on various pools
by executing "ceph osd pool set <pool-name> compression_mode aggressive".
Unfortunately, it seems like no data is compressed at all. As an example, below
is some diagnostic output for a data pool used by a cephfs:
[root@ceph-01 ~]# ceph --version
ceph version 12.2.7 (3ec878d1e53e1aeb47a9f619c49d9e7c0aa384d5) luminous (stable)
All defaults are OK:
[root@ceph-01 ~]# ceph --show-config | grep compression
[...]
bluestore_compression_algorithm = snappy
bluestore_compression_max_blob_size = 0
bluestore_compression_max_blob_size_hdd = 524288
bluestore_compression_max_blob_size_ssd = 65536
bluestore_compression_min_blob_size = 0
bluestore_compression_min_blob_size_hdd = 131072
bluestore_compression_min_blob_size_ssd = 8192
bluestore_compression_mode = none
bluestore_compression_required_ratio = 0.875000
[...]
Compression is reported as enabled:
[root@ceph-01 ~]# ceph osd pool ls detail
[...]
pool 24 'sr-fs-data-test' erasure size 8 min_size 7 crush_rule 10 object_hash
rjenkins pg_num 50 pgp_num 50 last_change 7726 flags hashpspool,ec_overwrites
stripe_width 24576 compression_algorithm snappy compression_mode aggressive
application cephfs
[...]
[root@ceph-01 ~]# ceph osd pool get sr-fs-data-test compression_mode
compression_mode: aggressive
[root@ceph-01 ~]# ceph osd pool get sr-fs-data-test compression_algorithm
compression_algorithm: snappy
We dumped a 4Gib file with dd from /dev/zero. Should be easy to compress with
excellent ratio. Search for a PG:
[root@ceph-01 ~]# ceph pg ls-by-pool sr-fs-data-test
PG_STAT OBJECTS MISSING_ON_PRIMARY DEGRADED MISPLACED UNFOUND BYTES LOG
DISK_LOG STATE STATE_STAMP VERSION REPORTED UP
UP_PRIMARY ACTING ACTING_PRIMARY LAST_SCRUB
SCRUB_STAMP LAST_DEEP_SCRUB DEEP_SCRUB_STAMP
24.0 15 0 0 0 0 62914560 77
77 active+clean 2018-09-14 01:07:14.593007 7698'77 7735:142
[53,47,36,30,14,55,57,5] 53 [53,47,36,30,14,55,57,5] 53
7698'77 2018-09-14 01:07:14.592966 0'0 2018-09-11 08:06:29.309010
There is about 250MB data on the primary OSD, but noting seems to be compressed:
[root@ceph-07 ~]# ceph daemon osd.53 perf dump | grep blue
[...]
"bluestore_allocated": 313917440,
"bluestore_stored": 264362803,
"bluestore_compressed": 0,
"bluestore_compressed_allocated": 0,
"bluestore_compressed_original": 0,
[...]
Just to make sure, I checked one of the objects' contents:
[root@ceph-01 ~]# rados ls -p sr-fs-data-test
10000000004.0000039c
[...]
10000000004.0000039f
It is 4M chunks ...
[root@ceph-01 ~]# rados -p sr-fs-data-test stat 10000000004.0000039f
sr-fs-data-test/10000000004.0000039f mtime 2018-09-11 14:39:38.000000, size
4194304
... with all zeros:
[root@ceph-01 ~]# rados -p sr-fs-data-test get 10000000004.0000039f obj
[root@ceph-01 ~]# hexdump -C obj
00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00400000
All as it should be, except for compression. Am I overlooking something?
Best regards,
=================
Frank Schilder
AIT Risø Campus
Bygning 109, rum S14
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