IBM General Parallel File System for AIX: Administration and Programming Reference

Changing GPFS disk states and parameters

You might find it necessary to change a disk's state if there is some indication of disk failure or if you need to restripe the file system. Refer to Displaying GPFS disk states for a detailed description of disk states. You can change both the availability and status of a disk using the mmchdisk command:

• Change disk availability using the mmchdisk command and the stop and start options
• Change disk status using the mmchdisk command and the suspend and resume options.

Issue the mmchdisk command with one of the following four options to change disk state:

suspend

Instructs GPFS to stop allocating space on the specified disk. Place a disk in this state prior to disk deletion or replacement. This is a user-initiated state that GPFS will never use without an explicit command to change disk state.

Note:

A disk remains suspended until it is explicitly resumed. Restarting GPFS or rebooting nodes does not restore normal access to a suspended disk.

resume

Informs GPFS that a disk previously suspended is now available for allocating new space. Resume a disk only when you've suspended it and decided not to delete or replace it. If the disk is currently in a stopped state, it remains stopped until you specify the start option. Otherwise, normal read and write access to the disk resumes.

stop

Instructs GPFS to stop any attempts to access the specified disk. Use this option to inform GPFS that a disk has failed or is currently inaccessible because of maintenance. A disk's availability remains down until it is explicitly started with the start option.

start

Informs GPFS that a disk previously stopped is now accessible. GPFS does this by first changing the disk availability from down to recovering. The file system metadata is then scanned and any missing updates (replicated data that was changed while the disk was down) are repaired. If this operation is successful, the availability is then changed to up.

If the metadata scan fails, availability is set to unrecovered. This could occur if other disks remain in recovering or an I/O error has occurred. Repair all disks (mmfsck) and paths to disks. The metadata scan can then be re-initiated at a later time by issuing the mmchdisk start command again.

If more than one disk in the file system is down, they should all be started at the same time by using the -a option. If you start them separately and metadata is stored on any disk that remains down, the mmchdisk start command fails.

For example, to suspend the gpfs5vsd disk in the file system fs1, enter:

mmchdisk fs1 suspend -d gpfsvsd5 

To confirm the change, enter:

mmlsdisk fs1

The system displays information similar to:

disk         driver   sector failure holds    holds
name         type       size   group metadata data  status        availability
------------ -------- ------ ------- -------- ----- ------------- ------------
gpfs4vsd    disk        512       2 yes      yes   ready         up   
gpfs5vsd    disk        512      -1 yes      yes   suspended     up           
    

You can also use the mmchdisk command with the change option to change the Disk Usage and Failure Group parameters for one or more disks in a GPFS file system. This can be useful in situations where, for example, a file system that contains only RAID disks is being upgraded to add conventional disks that are better suited to storing metadata. After adding the disks using the mmadddisk command, the metadata currently stored on the RAID disks would have to be moved to the new disks to achieve the desired performance improvement. To accomplish this, first the mmchdisk change command would be issued to change the Disk Usage parameter for the RAID disks to dataOnly. Then the mmrestripefs command would be used to restripe the metadata off the RAID device and onto the conventional disks.

For example, to specify that metadata should no longer be stored on disk gpfs5vsd , enter:

mmchdisk fs0 change -d "gpfs5vsd:::dataOnly"

To confirm the change, enter:

mmlsdisk fs1

The system displays information similar to:

disk         driver   sector failure holds    holds
name         type       size   group metadata data  status        availability
------------ -------- ------ ------- -------- ----- ------------- ------------
gpfs4vsd   disk        512       2 yes      yes   ready         up   
gpfs5vsd   disk        512      -1 no       yes   suspended     up           
    

See the mmchdisk Command and the mmlsdisk Command for complete usage information .