[lustre-discuss] re-registration of MDTs and OSTs

[Peter Grandi]

So I have been upgrading my one and only MDT to a larger ZFS
pool, by the classic route of creating a new pool, new MDT, and
then 'zfs send'/zfs receive' for the copy over (BTW for those
who may not be aware 'zfs send' output can be put into a file to
do offline backups of a Lustre ZFS filesystem instance).

At first I just created an empty MGT on the new devices (on a
server with the same NID as the old MGS), with the assumption
that given that MDTs and OSTs have unique (filesystem instance,
target type, index number) triples, with NIDs being just the
address to find the MGS, or where they can be found, they would
just register themselves with the MGT on startup.

But I found that there was a complaint that they were in a
registered state, and the MGT did not have their registration
entries. I am not sure that is the purpose of that check. So
I just copied over the old MGT where they were registered, and
all was fine.

* Is there a way to re-register MDTs and OSTs belonging to a
  given filesystem instance into a new different MGT?

* Is there a purpose to check whether MDTs and OSTs are or not
  registered in a given MGT?

* Is there a downside to register MDTs and OSTs in a different
  MGT from that which they were registered with initially?

My guess is that the MGT does not just contain the identities
and addresses of MDTs and OSTs of one or more filesystem
instance, but also a parameter list

If so, is there are way to dump the parameter for a filesystem
instance so it can be restored to a different MGT?