Delayed write operations
JFS allows you to defer updates of data into permanent storage. Delayed write operations save extra disk operations for files that are often rewritten.
You can enable the delayed write feature by opening the file with the deferred update flag, O_DEFER. This feature caches the data, allowing faster read and write operations from other processes.
When writing to files that have been opened with this flag, data is not
committed to permanent storage until a process issues the fsync command,
forcing all updated data to be committed to disk. Also, if a process issues
a synchronous write operation on a file, that is, the process has opened the
file with the O_SYNC flag, the operation is not deferred even if the
file was created with the O_DEFER flag.
Note: This feature is not
available for Enhanced JFS.