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authorJeremy Allison <jra@samba.org>2012-04-17 20:20:28 -0700
committerJeremy Allison <jra@samba.org>2012-04-18 07:20:19 +0200
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Add docs for aio_linux vfs module.
Autobuild-User: Jeremy Allison <jra@samba.org> Autobuild-Date: Wed Apr 18 07:20:19 CEST 2012 on sn-devel-104
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+<?xml version="1.0" encoding="iso-8859-1"?>
+<!DOCTYPE refentry PUBLIC "-//Samba-Team//DTD DocBook V4.2-Based Variant V1.0//EN" "http://www.samba.org/samba/DTD/samba-doc">
+<refentry id="vfs_aio_linux.8">
+
+<refmeta>
+ <refentrytitle>vfs_aio_linux</refentrytitle>
+ <manvolnum>8</manvolnum>
+ <refmiscinfo class="source">Samba</refmiscinfo>
+ <refmiscinfo class="manual">System Administration tools</refmiscinfo>
+ <refmiscinfo class="version">3.6</refmiscinfo>
+</refmeta>
+
+
+<refnamediv>
+ <refname>vfs_aio_linux</refname>
+ <refpurpose>implement async I/O in Samba vfs using Linux kernel aio calls</refpurpose>
+</refnamediv>
+
+<refsynopsisdiv>
+ <cmdsynopsis>
+ <command>vfs objects = aio_linux</command>
+ </cmdsynopsis>
+</refsynopsisdiv>
+
+<refsect1>
+ <title>DESCRIPTION</title>
+
+ <para>This VFS module is part of the
+ <citerefentry><refentrytitle>samba</refentrytitle>
+ <manvolnum>7</manvolnum></citerefentry> suite.</para>
+
+ <para>The <command>aio_linux</command> 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.</para>
+
+ <para>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.
+ </para>
+
+ <para>
+ Note that the smb.conf parameters <command>aio read size</command>
+ and <command>aio write size</command> must also be set appropriately
+ for this module to be active.
+ </para>
+
+ <para>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.</para>
+
+</refsect1>
+
+
+<refsect1>
+ <title>EXAMPLES</title>
+
+ <para>Straight forward use:</para>
+
+<programlisting>
+ <smbconfsection name="[cooldata]"/>
+ <smbconfoption name="path">/data/ice</smbconfoption>
+ <smbconfoption name="aio read size">1024</smbconfoption>
+ <smbconfoption name="aio write size">1024</smbconfoption>
+ <smbconfoption name="vfs objects">aio_linux</smbconfoption>
+</programlisting>
+
+</refsect1>
+
+<refsect1>
+ <title>OPTIONS</title>
+
+ <variablelist>
+
+ <varlistentry>
+ <term>aio_linux:aio num events = INTEGER</term>
+ <listitem>
+ <para>Set the maximum size of the event queue
+ that is used to limit outstanding IO requests.
+ </para>
+ <para>By default this is set to 128.</para>
+ </listitem>
+ </varlistentry>
+
+ </variablelist>
+</refsect1>
+<refsect1>
+ <title>VERSION</title>
+
+ <para>This man page is correct for version 3.6.6 of the Samba suite.
+ </para>
+</refsect1>
+
+<refsect1>
+ <title>AUTHOR</title>
+
+ <para>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.</para>
+
+</refsect1>
+
+</refentry>