11-14-2008
pstat -a shows, like for example ps aux, only the number of current started aioservers, but not if they are busy or not. With nmon shift+a you see how many are really currently busy and this is on system with an app using AIO, going up and down. Often the maxreqs is forgotten to be configured somewhat large too so the app doesn't get errors regarding to hit the max of queued AIO requests (some "error 5" in Oracle for example).
Nevertheless, we will have to check out if the OP needs AIO at all, which he could and should find out. Maybe he uses it already, no idea. Maybe he offers us some more info to help him.
In our environments I used CIO as a kind of last ressort of tuning, when everything else with AIO and ioo tuning didn't help anymore.
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LEARN ABOUT CENTOS
vfs_aio_linux
VFS_AIO_LINUX(8) System Administration tools VFS_AIO_LINUX(8)
NAME
vfs_aio_linux - implement async I/O in Samba vfs using Linux kernel aio calls
SYNOPSIS
vfs objects = aio_linux
DESCRIPTION
This VFS module is part of the samba(7) suite.
The aio_linux VFS module enables asynchronous I/O for Samba on Linux kernels that have the kernel AIO calls available without using the
Posix AIO interface. Posix AIO can suffer from severe limitations. For example, on some Linux versions the real-time signals that it uses
are broken under heavy load. Other systems only allow AIO when special kernel modules are loaded or only allow a certain system-wide amount
of async requests being scheduled. Systems based on glibc (most Linux systems) only allow a single outstanding request per file descriptor
which essentially makes Posix AIO useless on systems using the glibc implementation.
To work around all these limitations, the aio_linux module was written. It uses the Linux kernel AIO interface instead of the internal
Posix AIO interface to allow read and write calls to be processed asynchronously. A queue size of 128 events is used by default. To change
this limit set the "aio num events" parameter below.
Note that the smb.conf parameters aio read size and aio write size must also be set appropriately for this module to be active.
This module MUST be listed last in any module stack as the Samba VFS pread/pwrite interface is not thread-safe. This module makes direct
pread and pwrite system calls and does NOT call the Samba VFS pread and pwrite interfaces.
EXAMPLES
Straight forward use:
[cooldata]
path = /data/ice
aio read size = 1024
aio write size = 1024
vfs objects = aio_linux
OPTIONS
aio_linux:aio num events = INTEGER
Set the maximum size of the event queue that is used to limit outstanding IO requests.
By default this is set to 128.
VERSION
This man page is correct for version 4.0 of the Samba suite.
AUTHOR
The original Samba software and related utilities were created by Andrew Tridgell. Samba is now developed by the Samba Team as an Open
Source project similar to the way the Linux kernel is developed.
Samba 4.0 06/17/2014 VFS_AIO_LINUX(8)