Improving CephFS performance by always putting "default" data pool on SSDs? - ceph-users

4 Feb 2024

https://docs.ceph.com/en/reef/cephfs/createfs/ says:

...
  The data pool used to create the file system is the
“default” data pool and the location for storing all inode backtrace information, which is
used for hard link management and disaster recovery.
 For this reason, all CephFS inodes have at least one object in the default data pool. If
erasure-coded pools are planned for file system data, it is best to configure the default
as a replicated pool to improve small-object write and read performance when updating
backtraces. 
This poses the question:

Are normal replicated CephFS installations (metadata on SSDs, data on HDDs) set up with
suboptimal performance because they don't do this?

If having inodes/backtraces on replicated instead of EC improves performance,
shouldn't one expect that putting inodes/backtraces on SSD would improve it even
more?

From the docs I also cannot really conclude when inotes/backtraces become important.
Is that all the time, or only sometimes?

Thanks!