aio info

Richard Kearsley Richard.Kearsley at
Thu May 5 09:05:37 MSD 2011

A lot of talk about AIO recently - I actually didn't know it existed before, so I am trying it on freebsd8

# sysctl -a | grep aio
kern.features.aio: 1
vfs.aio.max_buf_aio: 16
vfs.aio.max_aio_queue_per_proc: 256
vfs.aio.max_aio_per_proc: 32
vfs.aio.unloadable: 0
vfs.aio.aiod_lifetime: 30000
vfs.aio.aiod_timeout: 10000
vfs.aio.num_buf_aio: 0
vfs.aio.num_queue_count: 0
vfs.aio.max_aio_queue: 1024
vfs.aio.target_aio_procs: 4
vfs.aio.num_aio_procs: 4
vfs.aio.max_aio_procs: 32

Could anyone comment what these mean and how to go about tweaking for best performance (should any be increased?)
Particularly.. vfs.aio.num_queue_count - does this monitor the amount of io waiting?

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