vfs_aio_pthread

Name

vfs_aio_pthread — implement async I/O in Samba vfs using a pthread pool

Synopsis

vfs objects = aio_pthread

DESCRIPTION

This VFS module is part of the + samba(7) suite.

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 glibc implementation.

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 interfaces.

EXAMPLES

Straight forward use:

+        [cooldata]
+	path = /data/ice
+	aio read size = 1024
+	aio write size = 1024
+	vfs objects = aio_pthread
+

OPTIONS

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.

VERSION

This man page is correct for version 3.6.3 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.