mmchfs command

Availability

Available on all IBM Spectrum Scale editions.

Description

Use the mmchfs command to change the attributes of a GPFS file system.

Parameters

Device

The device name of the file system to be changed.

File system names need not be fully qualified. fs0 is as acceptable as /dev/fs0. However, file system names must be unique across GPFS clusters.

This must be the first parameter.

-A {yes | no | automount}

Indicates when the file system is to be mounted:

yes

When the GPFS daemon starts.

no

The file system is mounted manually.

automount

On non-Windows nodes, when the file system is first accessed. On Windows nodes, when the GPFS daemon starts.

Note:

• The file system must be unmounted before the automount settings are changed.
• IBM Spectrum Protect for Space Management does not support file systems with the -A option set to automount.

-D {nfs4 | posix}

Specifies whether a deny-write open lock blocks writes, which is required by NFS V4, Samba, and Windows. File systems that support NFS V4 must have -D nfs4 set. The option -D posix allows NFS writes even in the presence of a deny-write open lock. If you intend to export the file system on NFS V4 or Samba, or mount your file system on Windows, you must use -D nfs4. For NFS V3 (or if the file system is not NFS exported at all) use -D posix.

-E {yes | no}

Specifies whether to report exact mtime values. If -E no is specified, the mtime value is periodically updated. If you want to always display exact modification times, specify -E yes.

Important: The new value takes effect the next time the file system is mounted.

-k {posix | nfs4 | all}

Specifies the type of authorization supported by the file system:

posix

Traditional GPFS ACLs only (NFS V4 and Windows ACLs are not allowed). Authorization controls are unchanged from earlier releases.

nfs4

Support for NFS V4 and Windows ACLs only. Users are not allowed to assign traditional GPFS ACLs to any file system objects (directories and individual files).

all

Any supported ACL type is permitted. This includes traditional GPFS (posix) and NFS V4 and Windows ACLs (nfs4).

The administrator is allowing a mixture of ACL types. For example, fileA may have a posix ACL, while fileB in the same file system may have an NFS V4 ACL, implying different access characteristics for each file depending on the ACL type that is currently assigned.

Avoid specifying nfs4 or all unless files are exported to NFS V4 or Samba clients, or the file system is mounted on Windows. NFS V4 and Windows ACLs affect file attributes (mode) and have access and authorization characteristics that are different from traditional GPFS ACLs.

-K {no | whenpossible | always}

Specifies whether strict replication is to be enforced:

no

Strict replication is not enforced. GPFS tries to create the needed number of replicas, but still returns EOK if it can allocate at least one replica.

whenpossible

Strict replication is enforced provided the disk configuration allows it. If there is only one failure group, strict replication is not enforced.

always

Strict replication is enforced.

For more information, see Strict replication.

-L LogFileSize

Specifies the size of the internal log files. The LogFileSize must be a multiple of the metadata block size. The default log file size is 32 MiB in most cases. However, if the data block size (parameter -B) is less than 512 KiB or if the metadata block size (parameter --metadata-block-size) is less than 256 KiB, then the default log file size is either 4 MiB or the metadata block size, whichever is greater. The minimum size is 256 KiB and the maximum size is 1024 MiB. Specify this value with the K or M character, for example: 8M. For more information, see mmcrfs command.

The default log size works well in most cases. An increased log file size is useful when the highly available write cache feature (parameter --write-cache-threshold) is enabled.

The new log file size is not effective until you apply one of the two following methods:

• The first method requires you in part to restart the GPFS daemon on the manager nodes, but you can do so one node at a time. Follow these steps:
  1. Restart the GPFS daemon (mmfsd) on all the manager nodes of the local cluster. This action is required even if the affected file system is not mounted on any of the manager nodes. You can do this action one manager node at a time.
  2. Remount the file system on all the local and remote nodes that have it mounted. You can do this action one node at a time. The new log file size becomes effective when the file system is remounted on the last affected node.
• The second method requires you to unmount the file system on all the affected nodes at the same time. Follow these steps:

  1. Unmount the file system on all local and remote nodes that have it mounted. The file system must be in the unmounted state on all the nodes at the same time.
  2. Remount the file system on any or all the affected nodes.

-m DefaultMetaDataReplicas

Changes the default number of metadata replicas. Valid values are 1, 2, and 3. This value cannot be greater than the value of MaxMetaDataReplicas set when the file system was created.

Changing the default replication settings using the mmchfs command does not change the replication setting of existing files. After running the mmchfs command, the mmrestripefs command with the -R option can be used to change all existing files or you can use the mmchattr command to change a small number of existing files.

-n NumNodes

Changes the number of nodes for a file system but does not change the existing system metadata structures. This setting is just an estimate and can be used only to affect the layout of the system metadata for storage pools created after the setting is changed.

-o MountOptions

Specifies the mount options to pass to the mount command when mounting the file system. For a detailed description of the available mount options, see Mount options specific to IBM Spectrum Scale.

-Q {yes | no}

If -Q yes is specified, quotas are activated automatically when the file system is mounted. If -Q no is specified, the quota files remain in the file system, but are not used.

For more information, see Enabling and disabling GPFS quota management.

-r DefaultDataReplicas

Changes the default number of data replicas. Valid values are 1, 2, and 3. This value cannot be greater than the value of MaxDataReplicas set when the file system was created.

Changing the default replication settings using the mmchfs command does not change the replication setting of existing files. After running the mmchfs command, the mmrestripefs command with the -R option can be used to change all existing files or you can use the mmchattr command to change a small number of existing files.

-S {yes | no | relatime}

Controls how the file attribute atime is updated.

Note: The attribute atime is updated locally in memory, but the value is not visible to other nodes until after the file is closed. To get an accurate value of atime, an application must call subroutine gpfs_stat or gpfs_fstat.

yes

The atime attribute is not updated. The subroutines gpfs_stat and gpfs_fstat return the time that the file system was last mounted with relatime=no. For more information, see the topics mmmount command with the -o parameter and Mount options specific to IBM Spectrum Scale.

no

The atime attribute is updated whenever the file is read. This option is the default if the minimum release level (minReleaseLevel) of the cluster is less than 5.0.0 when the file system is created.

relatime

The atime attribute is updated whenever the file is read, but only if one of the following conditions is true:

• The current file access time (atime) is earlier than the file modification time (mtime).
• The current file access time (atime) is greater than the atimeDeferredSeconds attribute. For more information, see mmchconfig command.

This setting is the default if the minimum release level (minReleaseLevel) of the cluster is 5.0.0 or greater when the file system is created.

For more information, see atime values.

-T Mountpoint

Change the mount point of the file system starting at the next mount of the file system.

The file system must be unmounted on all nodes before this command is issued.

-t DriveLetter

Changes the Windows drive letter for the file system.

The file system must be unmounted on all nodes before the command is issued.

-V {full | compat}

Changes the file system format to the latest format supported by the currently installed level of GPFS. This option might cause the file system to become permanently incompatible with earlier releases of GPFS.

Note: The -V option cannot be used to make file systems that were created earlier than GPFS 3.2.1.5 available to Windows nodes. Windows nodes can mount only file systems that were created with GPFS 3.2.1.5 or later.

Before issuing -V, see Upgrading. Ensure that all nodes in the cluster have been updated to the latest level of GPFS code and that you have successfully run the mmchconfig release=LATEST command.

For information about specific file system format and function changes when you upgrade to the current release, see File system format changes between versions of IBM Spectrum Scale.

full

Enables all new functionality that requires different on-disk data structures. Nodes in remote clusters that are running an earlier version of IBM Spectrum Scale will no longer be able to mount the file system. With this option the command fails if it is issued while any node that has the file system mounted is running an earlier version of IBM Spectrum Scale.

compat

Enables only backward-compatible format changes. Nodes in remote clusters that were able to mount the file system before the format changes can continue to do so afterward.

-W NewDeviceName

Assign NewDeviceName to be the device name for the file system.

-z {yes | no}

Enable or disable DMAPI on the file system. Turning this option on requires an external data management application such as IBM Spectrum Protect hierarchical storage management (HSM) before the file system can be mounted.

Note: IBM Spectrum Protect for Space Management does not support file systems with the -A option set to automount.

For further information regarding DMAPI for GPFS, see GPFS-specific DMAPI events.

--filesetdf

Specifies that when quotas are enforced for a fileset, the numbers reported by the df command are based on the quotas for the fileset (rather than the entire file system). This option affects the df command behavior only on Linux nodes.

--nofilesetdf

Specifies that when quotas are enforced for a fileset, the numbers reported by the df command are based on the quotas for the entire file system (rather than individual filesets).

--inode-limit MaxNumInodes[:NumInodesToPreallocate]

MaxNumInodes specifies the maximum number of files that can be created. Allowable values range from the current number of created inodes (determined by issuing the mmdf command with -F), through the maximum number of files possibly supported as constrained by the formula:

maximum number of files = (total file system space) / (inode size + subblock size)

Note: This formula works only for simpler configurations. For complex configurations, such as separation of data and metadata, this formula might not provide an accurate result.

If your file system has additional disks added or the number of inodes was insufficiently sized at file system creation, you can change the number of inodes and hence the maximum number of files that can be created.

For file systems that do parallel file creates, if the total number of free inodes is not greater than 5% of the total number of inodes, there is the potential for slowdown in file system access. Take this into consideration when changing your file system.

NumInodesToPreallocate specifies the number of inodes that are preallocated by the system right away. If this number is not specified, GPFS allocates inodes dynamically as needed.

The MaxNumInodes and NumInodesToPreallocate values can be specified with a suffix, for example 100K or 2M. Note that in order to optimize file system operations, the number of inodes that are actually created may be greater than the specified value.

This option applies only to the root fileset. When there are multiple inode spaces, use the --inode-space option of the mmchfileset command to alter the inode limits of independent filesets. The mmchfileset command can also be used to modify the root inode space. The --inode-space option of the mmlsfs command shows the sum of all inode spaces.

--log-replicas LogReplicas

Specifies the number of recovery log replicas. Valid values are 1, 2, 3, or DEFAULT. If DEFAULT is specified, the number of log replicas is the same as the number of metadata replicas currently in effect for the file system and changes when this number is changed.

Changing the default replication settings using the mmchfs command does not change the replication setting of existing files. After running the mmchfs command, the mmrestripefs command with the -R option can be used to change existing log files.

This option is applicable only if the recovery log is stored in the system.log storage pool. For more information about the system.log storage pool, see The system.log storage pool.

--maintenance-mode Device {yes [--wait] | no}

Turns file system maintenance mode on or off when you change file system attributes. The values are yes and no (the default).

Specifying --wait, which is valid only when you use it with the yes parameter, turns on the maintenance mode after you have unmounted the file system. If you specify yes without --wait and the file system is mounted, the command fails.

For more information on maintenance mode, see File system maintenance mode.

--mount-priority Priority

Controls the order in which the individual file systems are mounted at daemon startup or when one of the all keywords is specified on the mmmount command.

File systems with higher Priority numbers are mounted after file systems with lower numbers. File systems that do not have mount priorities are mounted last. A value of zero indicates no priority.

--perfileset-quota

Sets the scope of user and group quota limit checks to the individual fileset level, rather than to the entire file system.

--noperfileset-quota

Sets the scope of user and group quota limit checks to the entire file system, rather than to individual filesets.

--rapid-repair

Keeps track of incomplete replication on an individual file block basis (as opposed to the entire file). This may result in a faster repair time when very large files are only partially ill-replicated.

--norapid-repair

Specifies that replication status is kept on a whole file basis (rather than on individual block basis).

--write-cache-threshold HAWCThreshold

Specifies the maximum length (in bytes) of write requests that will be initially buffered in the highly-available write cache before being written back to primary storage. Only synchronous write requests are guaranteed to be buffered in this fashion.

A value of 0 disables this feature. 64K is the maximum supported value. Specify in multiples of 4K.

This feature can be enabled or disabled at any time (the file system does not need to be unmounted). For more information about this feature, see Highly available write cache (HAWC).

Exit status

0

Successful completion.

nonzero

A failure has occurred.

Security

You must have root authority to run the mmchfs command.

The node on which the command is issued must be able to execute remote shell commands on any other node in the cluster without the use of a password and without producing any extraneous messages. For more information, see Requirements for administering a GPFS file system.

See also

Location