Anthony's got it right. The RocksDB LZ4 compression will be incremental
as new compactions takes place. You can manually issue a full
compaction to trigger it if you'd like. If you want to switch back,
just remove the compression flag and restart the OSD. New SST files
will then be written out uncompressed.
Mark
On 8/9/25 5:35 PM, Anthony D'Atri wrote:
I *think* this will happen over time as each OSD’s RocksDB compacts, which might be incremental.
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.
I believe so.
Still the question remains on how to bring all existing data over to be compressed.
I think the only way is to rewrite the data. There are scripts out there to do this for CephFS, where the same process should work as can be used when migrating existing data to a new data pool. For RBD and RGW, re-write from a client. With RBD you might do something like
rbd export myimage | rbd import - myimage.new; rbd rm myimage ; rbd rename myimage.new myimage
dance, with caution regarding space, names, watchers, client attachments, phase of moon, etc.
With RGW maybe something like rclone or Chorus to copy into a new bucket, rm the old bucket.
Thanks!
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Best Regards,
Mark Nelson
Head of Research and Development
Clyso GmbH
p: +49 89 21552391 12 | a: Minnesota, USA
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