[Lustre-discuss] change netmask on MDS/OSS without downtime?

[Craig Prescott]

We are planning to add additional OSS nodes to one of our filesystems 
running Lustre 1.8.5.  The Lustre servers all offer o2ib and tcp (IPoIB) 
NIDs - our local IB clients use the o2ib NIDs, and some remote clients 
access the filesystem using the tcp NIDs via an ethernet-to-IB gateway. 
  The networks used by the tcp clients are routed.

We want to reconfigure our networks in a way that would impact the IPoIB 
networks on our Lustre servers.  We want to change network base 
addresses, netmasks, and broadcast addresses.  But we don't intend to 
change IP addresses (or NIDs) of the servers themselves.

Question is this - can we just do this live without unmounting either 
the clients or affected OSTs, thus avoiding a planned 
maintenance/outage?  I think we can, but LNET has surprised me before.

If we need to announce an outage for this, we will - but we only want to 
do that if it is actually necessary.

Thanks,
Craig Prescott
UF HPC Center