Thanks Greg and Steffen for your answer. I will make some tests.

Gregory Farnum wrote:

> Yeah. The metadata pool will contain:
> 1) MDS logs, which I think by default will take up to 200MB per
> logical MDS. (You should have only one logical MDS.)
> 2) directory metadata objects, which contain the dentries and inodes
> of the system; ~4KB is probably generous for each?

So one file in the cephfs generates one inode of ~4KB in the
"metadata" pool, correct? So that (number-of-files-in-cephfs) x 4KB
gives me an (approximative) estimation of the amount of data in the
"metadata" pool?

> 3) Some smaller data structures about the allocated inode range and
> current client sessions.
> 
> The data pool contains all of the file data. Presumably this is much
> larger, but it will depend on your average file size and we've not
> done any real study of it.

-- 
François Lafont
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