GPFS: Administration and Programming Reference - IRA Home

mmchattr Command
Name
mmchattr – Changes the replication attributes, storage pool assignment, and I/O caching policy for one or
more GPFS files.
Synopsis
mmchattr [-m MetadataReplicas] [-M MaxMetadataReplicas] [-r DataReplicas] [-R MaxDataReplicas] [-P
DataPoolName] [-D {yes | no} ] [-I {yes | defer}] Filename [Filename...]
Description
Use the mmchattr command to change the replication attributes, storage pool assignment, and I/O
caching policy for files in the GPFS file system.
The replication factor must be less than or equal to the maximum replication factor for the file. If
insufficient space is available in the file system to increase the number of replicas to the value requested,
the mmchattr command ends. However, some blocks of the file may have their replication factor
increased after the mmchattr command ends. If additional free space becomes available in the file system
at a later time (when, for example, you add another disk to the file system), you can then issue the
mmrestripefs command with the -r or -b option to complete the replication of the file. The mmrestripefile
command can be used in a similar manner. You can use the mmlsattr command to display the replication
values.
Data of a file is stored in a specific storage pool. A storage pool is a collection of disks or RAIDs with
similar properties. Because these storage devices have similar properties, you can manage them as a
groups. You can use storage pools to:
v Partition storage for the file system
v Assign file storage locations
v Improve system performance
v Improve system reliability
The Direct I/O caching policy bypasses file cache and transfers data directly from disk into the user space
buffer, as opposed to using the normal cache policy of placing pages in kernel memory. Applications with
poor cache hit rates or very large I/Os may benefit from the use of Direct I/O.
The mmchattr command can be run against a file in use.
You must have write permission for the files whose attributes you are changing.
Parameters
Filename [Filename ...] The name of one or more files to be changed. Delimit each file name by a
space. Wildcard characters are supported in file names, for example,
project*.sched.
Options
-D {yes | no}
Enable or disable the Direct I/O caching policy for files.
-I {yes | defer}
Specifies if replication and migration between pools is to be performed immediately (-I yes), or deferred
until a later call to mmrestripefs or mmrestripefile (-I defer). By deferring the updates to more than
one file, the data movement may be done in parallel. The default is -I yes.
Chapter 8. GPFS commands 81