MDS names may not start with a numeric digit.

[leseb]

Just spotted this:

deprecation warning: MDS id 'mds.7cf73bf1fd74' is invalid and will be forbidden in a future version. MDS names may not start with a numeric digit.

An easy work around could be to do something like this on the MDS_NAME variable: : ${MDS_NAME:=a$(hostname -s)}

[Ulexus]

I would slightly prefer a more mnemonic "mds-" prefix, but otherwise, that sounds like a good idea.

One thing to note, though, is that metadata servers are not machine-restricted. They are not bound by their data directories and can move around the cluster. As a result, I generally give mine labels like "a", "b", "c".

In this case, obviously, we cannot do that, but I wonder if adding and removing arbitrarily-named metadata servers screws with the Ceph database.

[leseb]

I like the "daemon type" prefix and I agree about the statement of volatile MDSs in general.
Perhaps we should encourage users to use MDS_NAME and justify this with your explanations.

Let's start by fixing this and we can always add a bit of doc later.