Release notes
https://ceph.io/en/news/blog/2024/v19-2-0-squid-released/#highlights say:
> BlueStore RocksDB LZ4 compression is now enabled by default to improve
> average performance and "fast device" space usage.
On one EC pool with many files I have such warnings:
osd.6 spilled over 8.0 GiB metadata from 'db' device (36 GiB used of 60
GiB) to slow device
and hope that the LZ4 compression might help with that.
What do I need to do to "migrate" my OSDs to that?
I already upgrade the cluster to Ceph 19.
Running
grep 'Options.compression: ' /var/log/ceph/ceph-osd.6.log
already shows the switch from
rocksdb: Options.compression: NoCompression
to
rocksdb: Options.compression: LZ4
in the logs.
But does restarting the OSDs already automtaically compress everything with
LZ4, or do I need to run some operation such as
ceph daemon osd.6 compact
or similar to make sure that existing data is actually compressed?
Also, could anybody clarify whether this setting is `compression_algorithm` from
https://docs.ceph.com/en/squid/rados/operations/pools/#setting-pool-values
https://docs.ceph.com/en/squid/rados/configuration/bluestore-config-ref/#confval-bluestore_compression_algorithm
or if that's something different (e.g. if that's "actual data" instead of
"metadata")?
I suspect it's different, because `ceph config show-with-defaults osd.6 | grep
compression` reveals:
bluestore_compression_algorithm snappy
bluestore_compression_mode none
bluestore_rocksdb_options
compression=kLZ4Compression,...
>From this it looks like `bluestore_compression*` is the "Inline compression"
>for data
>(https://docs.ceph.com/en/reef/rados/configuration/bluestore-config-ref/#inline-compression),
> and `bluestore_rocksdb_options` is what the "RocksDB compression" is about.
Still the question remains on how to bring all existing data over to be
compressed.
Thanks!
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