[lustre-discuss] MDT expansion

[Peter Grandi]

 > * Add a new MDT for DOM associated with a specific directory.

Just point out that this is a rather safe and perhaps preferable choice: 
one MDT without DOM, one with DOM, if setting up a new MDT/MDS is possible.

I guess that it would be possible to have two MDTs in the same MDS, but 
I haven't tried that yet.

> Note: adding "vdevs" to a "zpool" may not be necessarily what you want 
> to do, unless it is "zpool" of *mirror* "vdevs".

BTW for an MDT it really ought to be like that (RAID10 style).

Note: because of my bad luck I have had in the past to create an MDT on 
a "zpool" of a 'raidz1' of three devices, which is the one case that 
might be a less desirable but still somewhat acceptable alternative to a 
RAID10-style setup.

>> or do you recommend to stop Lustre beforehand?
> 
> I am about to post a question related to that. I think that the answer 
> is "not necessary", but I would "lct barrier_freeze"

Given the discussion in the other thread I guess stopping is not 
necessary, but freezing still is a good idea.