Enables or disables the use of asynchronous file I/O (AIO) on FreeBSD and Linux: location /video/ { aio on; output_buffers 1 64k; } On FreeBSD, AIO can be used starting from FreeBSD 4.3. Prior to FreeBSD 11.0, AIO can either be linked statically into a kernel: options VFS_AIO or loaded dynamically as a kernel loadable module: kldload aio On Linux, AIO can be used starting from kernel version 2.6.2