Now that the hybrid allocator appears to be enabled by default in Octopus, is it safe to change bluestore_min_alloc_size_hdd to 4k from 64k on Octopus 15.2.10 clusters, and then redeploy every OSD to switch to the smaller allocation size, without massive performance impact for RBD? We're seeing a lot of storage usage amplification on EC 8+3 clusters which are HDD backed that lines up with a lot of the mailing list posts we've seen here. Upgrading to Pacific before making this change is also a possibility once a more stable release arrives, if that's necessary. Second part of this question - we are using RBDs currently on the clusters impacted. These have XFS filesystems on top, which detect the sector size of the RBD as 512byte, and XFS has a block size of 4k. With the default of 64k for bluestore_min_alloc_size_hdd, let's say a 1G file is written out to the XFS filesystem backed by the RBD. On the ceph side, is this being seen as a lot of 4k objects thus a significant space waste is occurring, or is RBD able to coalesce these into 64k objects, even though XFS is using a 4k block size? XFS details below, you can see the allocation groups are quite large: meta-data=/dev/rbd0 isize=512 agcount=501, agsize=268435440 blks = sectsz=512 attr=2, projid32bit=1 = crc=1 finobt=1, sparse=1, rmapbt=0 = reflink=1 data = bsize=4096 blocks=134217728000, imaxpct=1 = sunit=16 swidth=16 blks naming =version 2 bsize=4096 ascii-ci=0, ftype=1 log =internal log bsize=4096 blocks=521728, version=2 = sectsz=512 sunit=16 blks, lazy-count=1 realtime =none extsz=4096 blocks=0, rtextents=0 I'm curious if people have been tuning XFS on RBD for better performance, as well. Thank you!