Oracle uses AIO on most operating systems. It implements it's own block and buffer cache so the kernel page cache just gets in the way. Since it does it's own b

Oracle uses AIO on most operating systems. It implements it's own block and buffer cache so the kernel page cache just gets in the way. Since it does it's own block cache, the block size and alignment limitations are not really a problem for it. KVM also uses AIO for similar reasons (guess OS has it's own page cache so we want to avoid double caching). AIO on Linux was basically designed for Oracle. Only a few classes of apps can really benefit from it. It also doesn't really guarantee to be non-blocking as many filesystem metadata operations do block (read the long threads on Linux mailing lists). Unless you're a special class of app that can live with the AIO limitations then you have to stick to blocking IO. Otherwise you're stuck rewriting the page cache and it's unlikely that you'll do a better job the the built in OS. I think Solaris has similar limitations compared to Linux. Windows has a better API with its async overlapped file API and even there various NTFS metadata operations can block.