Using Direct I/O on a file in a GPFS file system

The Direct I/O caching policy can be set for files in a GPFS file system by specifying the -D option on the mmchattr command.

This 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.

Direct I/O may also be specified by supplying the O_DIRECT file access mode on the open() of the file.