mmcrfs command

Availability

Available on all IBM Spectrum Scale editions.

Description

Use the mmcrfs command to create a GPFS file system. The first parameter must be Device and it must be followed by either DiskDescList or -F StanzaFile. You can mount a maximum of 256 file systems in an IBM Spectrum Scale cluster at any one time, including remote file systems.

The performance of a file system is affected by the values that you set for block size, replication, and the maximum number of files (number of inodes).

For information about replication factors, see the descriptions of the -m, -M, -r, and -R parameters in this help topic.

For information about the maximum number of files (number of inodes), see the description of the --inode-limit parameter later in this help topic.

Results

DiskName:::DiskUsage:FailureGroup::StoragePool:

Parameters

Device

The device name of the file system to be created.

File system names need not be fully qualified. fs0 is as acceptable as /dev/fs0. However, file system names must be unique within a GPFS cluster. Do not specify an existing entry in /dev.

This must be the first parameter.

"DiskDesc[;DiskDesc...]"

A descriptor for each disk to be included. Each descriptor is separated by a semicolon (;). The entire list must be enclosed in quotation marks (' or "). The use of disk descriptors is discouraged.

-F StanzaFile

Specifies a file that contains the NSD stanzas and pool stanzas for the disks that are to be added to the file system. NSD stanzas have the following format:

%nsd: 
  nsd=NsdName
  usage={dataOnly | metadataOnly | dataAndMetadata | descOnly}
  failureGroup=FailureGroup
  pool=StoragePool
  servers=ServerList
  device=DiskName
  thinDiskType={no | nvme | scsi | auto}

where:

nsd=NsdName

Specifies the name of an NSD that was previously created by the mmcrnsd command. For a list of available disks, issue the mmlsnsd -F command. This clause is mandatory for the mmcrfs command.

usage={dataOnly | metadataOnly | dataAndMetadata | descOnly}

Specifies the type of data that is to be stored on the disk.

Note: For information about the system storage pool, user storage pools, and the optional metadata system pool, see Internal storage pools.

dataAndMetadata

Indicates that the disk contains both data and metadata. This is the default for disks in the system pool.

dataOnly

Indicates that the disk contains data and does not contain metadata. This is the default for disks in storage pools other than the system pool.

metadataOnly

Indicates that the disk contains metadata and does not contain data.

descOnly

Indicates that the disk contains no data and no file metadata. IBM Spectrum Scale uses this type of disk primarily to keep a copy of the file system descriptor. It can also be used as a third failure group in certain disaster recovery configurations. For more information, see Synchronous mirroring with GPFS replication.

failureGroup=FailureGroup

Identifies the failure group to which the disk belongs. A failure group identifier can be a simple integer or a topology vector that consists of up to three comma-separated integers. The default is -1, which indicates that the disk has no point of failure in common with any other disk.

GPFS uses this information during data and metadata placement to ensure that no two replicas of the same block can become unavailable due to a single failure. All disks that are attached to the same NSD server or adapter must be placed in the same failure group.

If the file system is configured with data replication, all storage pools must have two failure groups to maintain proper protection of the data. Similarly, if metadata replication is in effect, the system storage pool must have two failure groups.

Disks that belong to storage pools in which write affinity is enabled can use topology vectors to identify failure domains in a shared-nothing cluster. Disks that belong to traditional storage pools must use simple integers to specify the failure group.

pool=StoragePool

Specifies the storage pool to which the disk is to be assigned. The default is the system storage pool. To specify the system storage pool explicitly, type system:

pool=system

Only the system storage pool can contain metadataOnly, dataAndMetadata, or descOnly disks. Disks in other storage pools must be dataOnly.

servers=ServerList

A comma-separated list of NSD server nodes. This clause is ignored by the mmcrfs command.

device=DiskName

The block device name of the underlying disk device. This clause is ignored by the mmcrfs command.

thinDiskType={no | nvme | scsi | auto}

Specifies the thin provisioned disk type:

Note: By default the system pool cannot contain both regular disks and thin provisioned disks. If you want to include both types of disk in the system pool, contact IBM Service for more information.

no

The disk is not thin provisioned. This value is the default.

nvme

The disk is a thin provisioned NVMe device that supports the mmreclaimspace command.

scsi

The disk is a thin provisioned SCSI disk that supports the mmreclaimspace command.

auto

The type of the disk is either nvme or scsi. IBM Spectrum Scale will try to detect the actual disk type automatically. To avoid problems, you should replace auto with the correct disk type, nvme or scsi, as soon as you can.

For more information, see IBM Spectrum Scale with data reduction storage devices.

Pool stanzas have the following format:

%pool: 
  pool=StoragePoolName
  blockSize=BlockSize
  usage={dataOnly | metadataOnly | dataAndMetadata}
  layoutMap={scatter | cluster}
  allowWriteAffinity={yes | no}
  writeAffinityDepth={0 | 1 | 2}
  blockGroupFactor=BlockGroupFactor

where:

pool=StoragePoolName

Is the name of a storage pool.

blockSize=BlockSize

Specifies the block size of the disks in the storage pool.

usage={dataOnly | metadataOnly | dataAndMetadata}

Specifies the type of data to be stored in the storage pool:

dataAndMetadata

Indicates that the disks in the storage pool contain both data and metadata. This is the default for disks in the system pool.

dataOnly

Indicates that the disks contain data and do not contain metadata. This is the default for disks in storage pools other than the system pool.

metadataOnly

Indicates that the disks contain metadata and do not contain data.

layoutMap={scatter | cluster}

Specifies the block allocation map type. When allocating blocks for a given file, GPFS first uses a round-robin algorithm to spread the data across all disks in the storage pool. After a disk is selected, the location of the data block on the disk is determined by the block allocation map type. If cluster is specified, GPFS attempts to allocate blocks in clusters. Blocks that belong to a particular file are kept adjacent to each other within each cluster. If scatter is specified, the location of the block is chosen randomly.

The cluster allocation method may provide better disk performance for some disk subsystems in relatively small installations. The benefits of clustered block allocation diminish when the number of nodes in the cluster or the number of disks in a file system increases, or when the file system's free space becomes fragmented. The cluster allocation method is the default for GPFS clusters with eight or fewer nodes and for file systems with eight or fewer disks.

The scatter allocation method provides more consistent file system performance by averaging out performance variations due to block location (for many disk subsystems, the location of the data relative to the disk edge has a substantial effect on performance). This allocation method is appropriate in most cases and is the default for GPFS clusters with more than eight nodes or file systems with more than eight disks.

The block allocation map type cannot be changed after the storage pool has been created.

allowWriteAffinity={yes | no}

Indicates whether the File Placement Optimizer (FPO) feature is to be enabled for the storage pool. For more information on FPO, see File Placement Optimizer

writeAffinityDepth={0 | 1 | 2}

Specifies the allocation policy to be used by the node writing the data.

A write affinity depth of 0 indicates that each replica is to be striped across the disks in a cyclical fashion with the restriction that no two disks are in the same failure group. By default, the unit of striping is a block; however, if the block group factor is specified in order to exploit chunks, the unit of striping is a chunk.

A write affinity depth of 1 indicates that the first copy is written to the writer node. The second copy is written to a different rack. The third copy is written to the same rack as the second copy, but on a different half (which can be composed of several nodes).

A write affinity depth of 2 indicates that the first copy is written to the writer node. The second copy is written to the same rack as the first copy, but on a different half (which can be composed of several nodes). The target node is determined by a hash value on the fileset ID of the file, or it is chosen randomly if the file does not belong to any fileset. The third copy is striped across the disks in a cyclical fashion with the restriction that no two disks are in the same failure group. The following conditions must be met while using a write affinity depth of 2 to get evenly allocated space in all disks:

1. The configuration in disk number, disk size, and node number for each rack must be similar.
2. The number of nodes must be the same in the bottom half and the top half of each rack.

This behavior can be altered on an individual file basis by using the --write-affinity-failure-group option of the mmchattr command.

This parameter is ignored if write affinity is disabled for the storage pool.

blockGroupFactor=BlockGroupFactor

Specifies how many file system blocks are laid out sequentially on disk to behave like a single large block. This option only works if --allow-write-affinity is set for the data pool. This applies only to a new data block layout; it does not migrate previously existing data blocks. For more information, see File Placement Optimizer.

-A {yes | no | automount}

Indicates when the file system is to be mounted:

yes

When the GPFS daemon starts. This is the default.

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

-B BlockSize

Specifies the size of data blocks in the file system. By default this parameter sets the block size and subblock size for all the data blocks and metadata blocks in the file system. This statement applies to all the data blocks and metadata blocks in the system storage pool and all the data blocks in user storage pools.

Note: You can specify a different size for metadata blocks and subblocks, and this setting can change the size and number of data subblocks. For more information see the description of the --metadata-block-size parameter later in this help topic.

Specify the value of the -B parameter with the character K or M. For example, to set the block size to 4 MiB with an 8 KiB subblock, type "-B 4M". The following table shows the supported block sizes with their subblock size:

Table 1. Supported block sizes with subblock size

Supported block sizes with subblock size
64 KiB block with a 2 KiB subblock
128 KiB block with a 4 KiB subblock
256 KiB, 512 KiB, 1 MiB, 2 MiB, or 4 MiB block with 8 KiB subblock
8 MiB or 16 MiB block with a 16 KiB subblock

Attention:

• A data block size of 4 MiB provides good sequential performance, makes efficient use of disk space, and provides good performance for small files. It works well for the widest variety of workloads.
• For information about suggested block sizes for different types of I/O and for different workloads and configuration types, see Block size.

Default block size

If the -B parameter is not specified then the data blocks and the metadata blocks in the file system are set to a default block size and subblock size. If the format version of the file system is 5.0.0 or greater (and the value of the maxblocksize cluster attribute is greater than 4 MiB) then the default block size is 4 MiB with an 8 KiB subblock.

The default block size depends on the file system format version of the new file system, which is determined by the specified value or the default value of the --version parameter. For more information, see the description of the --version parameter later in this help topic.

• If the format version of the new file system is 5.0.0 or greater (available in IBM Spectrum Scale 5.0.x or later) then the following settings apply:
  • The default block size is 4 MiB or the value of the maxblocksize attribute of the cluster, whichever is smaller. For more information about the maxblocksize attribute, see mmchconfig command.
    Note: But if maxblocksize is less than 256 KiB, then you must explicitly set -B BlockSize to 64 KiB or 128 KiB.
  • The subblock size is set from the appropriate row of Table 1.
• If the format version of the file system is earlier than 5.0.0 (earlier than IBM Spectrum Scale 5.0.0) then the following settings apply:
  • The default block size is 256 KiB.
  • The subblock size is 1/32 of the block size.

Subblocks

By default the data blocks and metadata blocks in a file system are set to the same block size and the same subblock size. The block size and subblock size are determined either by a setting from Table 1 (if -B is specified) or by the default sizes (if -B is not specified).

However, if metadata blocks are set to a different size than data blocks by the --metadata-block-size parameter, which is described later in this help topic, the following steps are taken automatically to determine the subblock sizes for data blocks and metadata blocks:

1. Determine the number of subblocks. This step is necessary because data blocks and metadata blocks must have the same number of subblocks:
   1. Choose the block type with the smaller block size (usually the metadata block).
   2. Set the subblock size from the appropriate row in Table 1.
   3. Find the number of subblocks by dividing the block size by the subblock size. This value will be the number of subblocks for both data blocks and metadata blocks.
   For example, suppose that initially the block sizes are set to 16 MiB for data blocks and 1 MiB for metadata blocks. The smaller block size is 1 MiB for metadata blocks. From Table 1, the subblock size for a block size of 1 MiB is 8 KiB. Therefore the number of subblocks is (1 MiB / 8 KiB) or 128 subblocks. Thus the following settings are determined:

   • For metadata blocks, from the table, the block size is 1 MiB and the metadata subblock size is 8 KiB.
   • Both data blocks and metadata blocks must have 128 subblocks.

2. Determine the subblock size for the other block type (usually the data block) by dividing the block size by the number of subblocks from Step 1. Continuing the example from Step 1, a data block must have 128 subblocks. Therefore the subblock size for data blocks is (16 MiB / 128) or 128 KiB. Note that this is different than the standard subblock size of 16 KIB for a 16 MIB block.

-D {nfs4 | posix}

Specifies whether a deny-write open lock blocks write operations, as it is required to do by NFS V4. File systems supporting 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 using NFS V4 or Samba, you must use -D nfs4. For NFS V3 (or if the file system is not NFS exported at all) use -D posix. The default is -D nfs4.

-E {yes | no}

Specifies whether to report exact mtime values (-E yes), or to periodically update the mtime value for a file system (-E no). If it is more desirable to display exact modification times for a file system, specify or use the default -E yes.

-i InodeSize

Specifies the byte size of inodes. Supported inode sizes are 512, 1024, and 4096 bytes. The default is 4096.

-j {cluster | scatter}

Specifies the default block allocation map type to be used if layoutMap is not specified for a given storage pool.

-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 might 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. The default is -k all.

Avoid specifying nfs4 or all unless files are to be 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

Indicates that 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

Indicates that strict replication is enforced provided the disk configuration allows it. If the number of failure groups is insufficient, strict replication is not enforced. This is the default value.

always

Indicates that strict replication is enforced.

For more information, see the topic "Strict replication" in the IBM Spectrum Scale: Problem Determination Guide.

-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.

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.

-m DefaultMetadataReplicas

Specifies the default number of copies of inodes, directories, and indirect blocks for a file. Valid values are 1, 2, and 3. This value cannot be greater than the value of MaxMetadataReplicas. The default is 1.

-M MaxMetadataReplicas

Specifies the default maximum number of copies of inodes, directories, and indirect blocks for a file. Valid values are 1, 2, and 3. This value cannot be less than the value of DefaultMetadataReplicas. The default is 2.

-n NumNodes

The estimated number of nodes that will mount the file system in the local cluster and all remote clusters. This is used as a best guess for the initial size of some file system data structures. The default is 32. This value can be changed after the file system has been created but it does not change the existing data structures. Only the newly created data structure is affected by the new value. For example, new storage pool.

When you create a GPFS file system, you might want to overestimate the number of nodes that will mount the file system. GPFS uses this information for creating data structures that are essential for achieving maximum parallelism in file system operations (For more information, see GPFS architecture ). If you are sure there will never be more than 64 nodes, allow the default value to be applied. If you are planning to add nodes to your system, you should specify a number larger than the default.

-Q {yes | no}

Activates quotas automatically when the file system is mounted. The default is -Q no. Issue the mmdefedquota command to establish default quota values. Issue the mmedquota command to establish explicit quota values.

To activate GPFS quota management after the file system has been created:

1. Mount the file system.
2. To establish default quotas:
   1. Issue the mmdefedquota command to establish default quota values.
   2. Issue the mmdefquotaon command to activate default quotas.
3. To activate explicit quotas:
   1. Issue the mmedquota command to activate quota values.
   2. Issue the mmquotaon command to activate quota enforcement.

-r DefaultDataReplicas

Specifies the default number of copies of each data block for a file. Valid values are 1, 2, and 3. This value cannot be greater than the value of MaxDataReplicas. The default is 1.

-R MaxDataReplicas

Specifies the default maximum number of copies of data blocks for a file. Valid values are 1, 2, and 3. This value cannot be less than the value of DefaultDataReplicas. The default is 2.

-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

Specifies the mount point directory of the GPFS file system. If it is not specified, the mount point is set to DefaultMountDir/Device. The default value for DefaultMountDir is /gpfs but, it can be changed with the mmchconfig command.

-t DriveLetter

Specifies the drive letter to use when the file system is mounted on Windows.

-v {yes | no}

Verifies that specified disks do not belong to an existing file system. The default is -v yes. Specify -v no only when you want to reuse disks that are no longer needed for an existing file system. If the command is interrupted for any reason, use -v no on the next invocation of the command.

Important: Using -v no on a disk that already belongs to a file system will corrupt that file system. This will not be noticed until the next time that file system is mounted.

-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. The default is -z no.

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

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

--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. This is the default.

--inode-limit MaxNumInodes[:NumInodesToPreallocate]

Specifies the maximum number of files in the file system.

In a file system that does parallel file creates, the number of free inodes must be greater than 5% of the total number of inodes. If not, the performance of the file system can be degraded. To increase the number of inodes, issue the mmchfs command.

The parameter NumInodesToPreallocate specifies the number of inodes that the system immediately preallocates. If you do not specify a value for NumInodesToPreallocate, GPFS dynamically allocates inodes as needed.

You can specify the NumInodes and NumInodesToPreallocate values 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.

--log-replicas LogReplicas

Specifies the number of recovery log replicas. Valid values are 1, 2, 3, or DEFAULT. If not specified, or 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.

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.

--metadata-block-size MetadataBlockSize

Sets the metadata block size. Setting the metadata block size to a smaller value than the data block size can improve file system performance, especially when the data block size is greater than 1 MiB.

By default the data blocks and metadata blocks in a file system are set to the same block size and the same subblock size. For more information about these settings see the description of the -B BlockSize parameter earlier in this help topic.

To set metadata blocks to a different size than data blocks, you must define a metadata-only system pool and specify the --metadata-block-size parameter when you issue the mmcrfs command. Follow these steps:

1. Define a pool stanza for a metadata-only system pool. Include the following settings:
   • Set pool to a valid pool name.
   • Do not set a value for blockSize. The metadata block size is set in the --metadata-block-size parameter of the mmcrfs command.
   • Set usage to metadataOnly.
2. Define an NSD stanza that includes the following settings:
   • Set usage to metadataOnly.
   • Set pool to the name of the pool stanza that you defined in Step 1.
3. Include the NSD stanza and the pool stanza in the stanza file that you will pass to the mmcrfs command.
4. When you run the mmcrfs command, include the --metadata-block-size parameter and specify a valid block size from Table 1.

Note: When metadata blocks are set to a different size than data blocks, the subblock sizes are ultimately determined by an automatic sequence of steps in the mmcrfs command processing. For more information see the "Subblocks" subtopic in the description of the --B BlockSize parameter earlier in this help topic.

--perfileset-quota

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

--noperfileset-quota

Sets the scope of user and group quota limit checks to the entire file system (rather than per individual fileset). This is the default.

--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. This is the default.

--version VersionString

Specifies the file system format version of the new file system, such as 4.2.3.0. A file system format version is associated with a file system format number (for example, 17.0) that determines the features that are enabled in the new file system. For more information about these values, see File system format changes between versions of IBM Spectrum Scale.

If you do not specify this parameter, the file system format version of the new file system defaults to the version of IBM Spectrum Scale that is installed on the node where you issue the command. For example, if IBM Spectrum Scale version 4.2.3 is installed on the node where you issue the command, then the default file system format version for the new file system is 4.2.3.0.

Whether you specify the file system format version or let it assume the default value, the file system format version must be in the range 4.1.1.0 - mRL, where mRL is the minimum release level of the cluster (minReleaseLevel).

The file system format version also affects the default value of the -B BlockSize parameter. For more information, see the description of that parameter earlier in this help topic.

Important:

• A remote node with an installed product version of IBM Spectrum Scale (for example, 4.2.3) that is less than the file system format version of the new file system (such as 5.0.0) will not be able to access the file system.
• Windows nodes can mount only file systems with a file system format version greater than or equal to 3.2.1.5.
• If you do not specify this parameter and the installed product version of the node where you issue the command is greater than the minimum release level (minReleaseLevel) of the cluster, then the command returns with an error message and prompts you to upgrade the minimum release level. To avoid this result, specify a file system format version with the --version parameter.
• In many contexts you might want to let the file system format version assume its default value. However, specifying an explicit file system format version can be useful or necessary in the following contexts:
  • When nodes in the cluster are running different versions of IBM Spectrum Scale.
  • When you want to make the file system available to remote clusters in which nodes are running an earlier version of IBM Spectrum Scale.

--profile ProfileName

Specifies a predefined profile of attributes to be applied. System-defined profiles are located in /usr/lpp/mmfs/profiles/. All the file system attributes listed under a file system stanza are changed as a result of this command. The following system-defined profile names are accepted:

• gpfsProtocolDefaults
• gpfsProtocolRandomIO

The file system attributes are applied at file system creation. If there is a current profile in place on the system (use mmlsconfig profile to check), then the file system is created with those attributes and values listed in the profile's file system stanza. The default is to use whatever attributes and values associate with the current profile setting.

Furthermore, any and all file system attributes from an installed profile file can be by-passed with '--profile=userDefinedProfile', where the userDefinedProfile is a profile file has been installed by the user in /var/mmfs/etc/.

User-defined profiles consist of the following stanzas:

%cluster:
[CommaSeparatedNodesOrNodeClasses:]ClusterConfigurationAttribute=Value
...
%filesystem:
FilesystemConfigurationAttribute=Value
...

A sample file can be found in /usr/lpp/mmfs/samples/sample.profile. See the mmchconfig command for a detailed description of the different configuration parameters.

User-defined profiles should be used only by experienced administrators. When in doubt, use the mmchconfig command instead.

--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

Security

You must have root authority to run the mmcrfs 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

/usr/lpp/mmfs/bin