Direct I/O allows an application to transfer data directly to disk from an application buffer and vice versa.
Data does not pass through the filesystem cache
Data is transferred by DMA and does not involve CPU overhead
Synchronous I/O
XFS allows for parallel writes to same file
Uses of direct I/O
Backup programs, so that they can work without polluting the page cache
Applications that need 'intelligent' caching
High performance, bandwidth intensive workloads
