vfs_aio_pthread - implement async I/O in Samba vfs using a pthread pool
vfs objects =
This VFS module is part of the samba
The aio_pthread VFS module enables asynchronous I/O for Samba on platforms which
have the pthreads API 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
To work around all these limitations, the aio_pthread module was written. It
uses a pthread pool instead of the internal Posix AIO interface to allow read
and write calls to be process asynchronously. A pthread pool is created which
expands dynamically by creating new threads as work is given to it to a
maximum of 100 threads per smbd process. To change this limit see the
"aio num threads" parameter below. New threads are not created if
idle threads are available when a new read or write request is received, the
new work is given to an existing idle thread. Threads terminate themselves if
idle for one second.
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
Straight forward use:
path = /data/ice
aio read size = 1024
aio write size = 1024
vfs objects = aio_pthread
aio_pthread:aio num threads = INTEGER
Limit the maximum number of threads per smbd
that will be created in the thread pool to service IO requests.
By default this is set to 100.
This man page is correct for version 4.0 of the Samba suite.
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.