[donavanm]

Last I looked (~4.4) linux AIO implied DIO. Conflating aio and dio is the problem, not a feature. On FreeBSD AIO works with the page cache for read and write, read ahead works, sendfile works, io & cache & readahead & size hints all work. Linux has half of those, and DIO none. As i recall.

[tatersolid]

Bingo. Async disk IO on Linux has to be unbuffered and block aligned. Making it useful only for databases that manage their own caching, and useless for file systems.

A video CDN needs lots of concurrent access to a file system.