GPFS: Administration and Programming Reference - IRA Home

v You must identify the disks by the NSD names that were given to them by the mmcrnsd command.
v You must explicitly specify values for both the primary and backup NSD server nodes even if you are
only changing one of them.
v The file system that contains the NSD being changed must be unmounted prior to issuing the
mmchnsd command.
v The NSD must be properly connected to the new nodes prior to issuing the mmchnsd command.
v This command cannot be used to change the DiskUsage or FailureGroup for an NSD. You must issue
the mmchdisk command to change these.
v You cannot change the name of the NSD.
For example, to assign node k145n07 as a backup NSD server for disk gpfs47nsd:
1. Since you must always specify the primary, first issue the mmlsnsd command to ensure you are not
inadvertently changing the primary server.
mmlsnsd -d "gpfs47nsd"
The system displays information similar to:
File system Disk name Primary node Backup node
---------------------------------------------------------------
fs1 gpfs47nsd k145n06
2. Unmount the file system on all nodes and ensure that the disk is connected to the new node k145n07.
3. Next issue the mmchnsd command:
mmchnsd "gpfs47nsd:k145n06:k145n07"
4. Verify the changes by issuing the mmlsnsd command:
mmlsnsd -d "gpfs47nsd"
The system displays information similar to:
File system Disk name Primary node Backup node
---------------------------------------------------------------
fs1 gpfs47nsd k145n06 k145n07
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 /dev block device interfaces for virtual shared disk, 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:
34 GPFS: Administration and Programming Reference