Changing NSD server usage and failback

GPFS determines if a node has physical or virtual connectivity to an underlying NSD disk through a sequence of commands invoked from the GPFS daemon. This determination is called disk discovery and occurs at both initial GPFS startup as well as whenever a file system is mounted.

The default order of access used in disk discovery:
  1. Local block device interfaces for SAN, SCSI or IDE disks
  2. NSD servers
The useNSDserver file system mount option can be used to set the order of access used in disk discovery, and limit or eliminate switching from local access to NSD server access, or the other way around. This option is specified using the -o flag of the mmmount, mount, mmchfs, and mmremotefs commands, and has one of these values:
always
Always access the disk using the NSD server.
asfound
Access the disk as found (the first time the disk was accessed). No change of disk access from local to NSD server, or the other way around, is performed by GPFS.
asneeded
Access the disk any way possible. This is the default.
never
Always use local disk access.
For example, to always use the NSD server when mounting file system fs1, issue this command: 
mmmount fs1 -o useNSDserver=always
To change the disk discovery of a file system that is already mounted: cleanly unmount it, wait for the unmount to complete, and then mount the file system using the desired -o useNSDserver option.