GPFS: Administration and Programming Reference - IRA Home

Restriping offers the opportunity to specify useful options in addition to rebalancing (-b option).
Re-replicate (-r option) provides for proper replication of all data and metadata. 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 expect delays in
replacing the failed disk, you could protect against data loss by suspending the failed disk using the
mmchdisk command and re-replicating. This would assure that all data existed in two copies on
operational disks.
If files are assigned to one storage pool, but with data in a different pool, the placement (-p) option will
migrate their data to the correct pool. Such files are referred to as ill-placed. Utilities, such as the
mmchattr command, may change a file’s storage pool assignment, but not move the data. The
mmrestripefs command may then be invoked to migrate all of the data at once, rather than migrating
each file individually. Note that the rebalance (-b) option also performs data placement on all files,
whereas the placement (-p) option rebalances only the files that it moves.
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 error logs show 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 re-replicate (-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 re-replicating 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 data copying and may
affect system performance. Plan to perform this task when system demand is low.
When using SANergy, consider these points:
v If the mmrestripefs command is issued on a file that is locked by SANergy, the command waits until it
is unlocked before proceeding.
v I/O operations from SANergy clients must terminate before using the mmrestripefs command. If not,
the client applications receive an error.
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” on page 32.
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” on page 31.
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:
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 ...
20 GPFS: Administration and Programming Reference