Hello everyone,

We have an existing LFS that is dual-homed on ethernet (mainly for our 
workstations) and IB (for the computational cluster), ZFS backend for the MDT 
and OST's.  We just got a new computational cluster and need to add another IB 
NID.  The procedure for doing this is straight forward (14.5 in the admin 
manual) and amounts to:

Unmount the clients
Unmount the MDT
Unmount all OSTs
mount -t lustre MDT partition -o nosvc mount_point
lctl replace_nids devicename nid1[,nid2,nid3 ...]

We haven't had to update a NID in a while so I was happy to see you can do this 
with "lctl replace_nids" instead of "tunsfs.lustre --writeconf".

I know this is dangerous, but we will sometime make minor changes to the 
servers by unmounting lustre on the servers (but leaving the clients up), make 
the changes, then remount the servers.  If we are confident we can do this 
quickly, the clients recover just fine.

While this isn't such a minor change, I'm a little tempted to do that in this 
case since nothing will really change for the existing clients – they don't 
need the new NID.  Am I asking for trouble here or do you think I can get away 
with this?  I'm not too concerned about the possibility of it taking too long 
and getting the existing clients evicted.   I'm (obviously) more concerned 
about doing something that would lead to corrupting the FS.  I should probably 
schedule an outage and do this right but... :)

Darby
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