Asynchronous auto prefetch for AFM NFS-based filesets

Asynchronous auto prefetch synchronizes created, modified, or deleted data from the home cluster to the AFM cache fileset at specified intervals. This automatic synchronization provides quick insights to AI applications, reduces costs, improves performance, enhances security, and streamlines operations.

Asynchronous auto prefetch synchronizes data changes from the home cluster to an AFM cache fileset at regular intervals. When you set the afmAsyncPrefetchInterval parameter, the system detects file and directory creations, modifications, and deletions on the home cluster and replicates them to the cache. This feature is available for filesets in independent writer (IW) and read-only (RO) modes. For cloud object storage filesets, see Asynchronous auto prefetch.

Configuration parameters

The afmAsyncPrefetchInterval parameter controls the synchronization interval. Set this parameter by using the mmchfileset command for existing filesets or the mmcrfileset command during the creation of a fileset.

  • The default value is disabled.
  • The recommended value is 30 minutes.
  • The valid range is 0 to 2147483647 minutes.

Watch folder integration

When you enable clustered watch folder for an AFM fileset in the RO or IW mode, the system generates event notifications for file and directory operations. The clustered watch folder detects file system activities such as creation, deletion, modification at the AFM fileset level and streams notifications to an external message queue. For more information, see Introduction to clustered watch folder.

Watch folder events are generated at the cache cluster when the asynchronous prefetch process downloads changed metadata and data from the home cluster. For each change on the home cluster, the cache fileset creates or updates the corresponding file or directory. Deletions on the home cluster trigger corresponding deletions on the cache.

Example: Setting an asynchronous prefetch interval for existing filesets

mmchfileset fs1 afmRO1 -p afmAsyncPrefetchInterval=60

A sample output is as follows:

Fileset afmRO1 changed.

This command sets the asynchronous prefetch interval to 60 minutes for the afmRO1 fileset in the fs1 file system.

Example: Setting an asynchronous prefetch interval during the creation of a fileset

mmcrfileset fs1 afmRO1 -p afmtarget=home1:/gpfs/fs1/export1 \
  --inode-space=new --inode-limit=10000 \
  -p afmmode=ro,afmFileOpenRefreshInterval=disable,\
afmFileLookupRefreshInterval=disable,\
afmDirOpenRefreshInterval=disable,\
afmDirLookupRefreshInterval=disable,\
afmAsyncPrefetchInterval=60

A sample output is as follows:

Fileset afmRO1 created with id 5 root inode 2097155.

This command creates a new AFM read-only fileset with an asynchronous prefetch interval set to 60 minutes. The fileset is configured with:

  • The home1:/gpfs/fs1/export1 target path.
  • AFM mode is read-only (RO).
  • All refresh intervals are disabled.
  • Asynchronous prefetch interval set to 60 minutes.

Example: Verifying asynchronous prefetch interval settings

mmlsfileset fs1 afmRO1 --afm -L
A sample output is as follows:
Filesets in file system 'fs1':

Attributes for fileset afmRO1:
======================================
Status                                  Linked
Path                                    /gpfs/fs1/afmRO1
Id                                      5
Root inode                              2097155
Parent Id                               0
Created                                 Wed May 13 18:54:23 2026
Comment                                 
Inode space                             4      
Maximum number of inodes                10000
Allocated inodes                        10000
Permission change flag                  chmodAndSetacl
afm-associated                          Yes
Target                                  home1:/gpfs/fs1/export1
Mode                                    read-only
File Lookup Refresh Interval            disable
File Open Refresh Interval              disable
Dir Lookup Refresh Interval             disable
Dir Open Refresh Interval               disable
Async Delay                             15 (default)
Async Prefetch Interval                 60
Last pSnapId                            0
Display Home Snapshots                  no
Number of Gateway Flush Threads         4
Prefetch Threshold                      0 (default)
Eviction Enabled                        yes (default)
IO Flags                                0x0 (default)
Note: The asynchronous prefetch interval is set to 60 minutes. The system synchronizes changes from the home cluster every 60 minutes.

For more information about configuration, see Configuring asynchronous auto prefetch for AFM filesets with NFS targets

Benefits

Asynchronous auto prefetch provides the following benefits:
Reduced latency
Applications access current data from the local cache instead of the remote home cluster.
Lower network usage
Only changed data transfers between clusters to reduce bandwidth consumption.
Simplified operations
Synchronization occurs automatically at the configured interval without manual data transfers.
Consistent data access
Multiple applications use the same synchronized cache to maintain consistent data across workloads.

Requirements and limitations

  • Available only for filesets in IW and RO modes.
  • The afmAsyncPrefetchInterval parameter is disabled by default. Set a value to enable synchronization.