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

Restriping a GPFS file system

Writing data into a GPFS file system correctly stripes the file. However, if you have added disks to a GPFS file system that is seldom updated, you can restripe the file system to achieve maximum performance using the mmrestripefs command.

Restriping offers the opportunity to specify useful options in addition to rebalancing (the -b option). Rereplicate (-r option) insures that all data and metadata is properly replicated. If you use replication, this option is useful to protect against additional failures after losing a disk. For example, if you use a replication factor of 2 and one of your disks fails, only a single copy of the data would remain. If another disk then failed before the first failed disk was replaced, some data might be lost. If you expected delays in replacing the failed disk, you could protect against data loss by suspending the failed disk using the mmchdisk command and rereplicating. This would assure that all data existed in two copies on operational disks.

If you do not replicate all of your files, the migrate (-m) option is useful to protect against data loss when you have an advance warning that a disk may be about to fail, for example, when the AIX error log shows an excessive number of I/O errors on a disk. Suspending the disk and issuing the mmrestripefs command with the -m option is the quickest way to migrate only the data that would be lost if the disk failed.

If you do not use replication, the -m and -r options are equivalent; their behavior differs only on replicated files. After a successful rereplicate (-r option) all suspended disks are empty. A migrate operation, using the -m option, leaves data on a suspended disk as long as at least one other replica of the data remains on a disk that is not suspended. Restriping a file system includes rereplicating it; the -b option performs all the operations of the -m and -r options.

Consider the necessity of restriping and the current demands on the system. New data which is added to the file system is correctly striped. Restriping a large file system requires extensive insert and delete operations and may affect system performance. Plan to perform this task when system demand is low.

If you are sure you want to proceed with the restripe operation:

1. Use the mmchdisk command to suspend any disks to which you do not want the file system restriped. You may want to exclude disks from file system restriping because they are failing (see Changing GPFS disk states and parameters).
2. Use the mmlsdisk command to assure that all disk devices to which you do want the file system restriped are in the up/normal state (see Displaying GPFS disk states).

Specify the target file system with the mmrestripefs command. For example, to rebalance (-b option) file system fs2 after adding an additional RAID device, enter:

mmrestripefs fs2 -b

The system displays information similar to:

(16:46:06) k145n02:/fs2 # mmrestripefs fs2 -b
GPFS: 6027-589 Scanning file system metadata, phase 1 ... 
  48 % complete on Wed Aug 16 16:47:53 2000
  96 % complete on Wed Aug 16 16:47:56 2000
 100 % complete on Wed Aug 16 16:47:56 2000
GPFS: 6027-552 Scan completed successfully.
GPFS: 6027-589 Scanning file system metadata, phase 2 ... 
GPFS: 6027-552 Scan completed successfully.
GPFS: 6027-589 Scanning file system metadata, phase 3 ... 
  98 % complete on Wed Aug 16 16:48:02 2000
 100 % complete on Wed Aug 16 16:48:02 2000
GPFS: 6027-552 Scan completed successfully.
GPFS: 6027-565 Scanning user file metadata ...
GPFS: 6027-552 Scan completed successfully.
 

See the mmrestripefs Command for complete usage information.