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| 2 | .\" Title: vfs_aio_linux
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| 3 | .\" Author: [see the "AUTHOR" section]
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| 4 | .\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
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| 5 | .\" Date: 10/25/2016
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| 6 | .\" Manual: System Administration tools
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| 7 | .\" Source: Samba 4.4
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| 8 | .\" Language: English
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| 9 | .\"
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| 10 | .TH "VFS_AIO_LINUX" "8" "10/25/2016" "Samba 4\&.4" "System Administration tools"
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| 11 | .\" -----------------------------------------------------------------
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| 12 | .\" * Define some portability stuff
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| 13 | .\" -----------------------------------------------------------------
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| 14 | .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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| 15 | .\" http://bugs.debian.org/507673
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| 16 | .\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
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| 21 | .\" * set default formatting
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| 27 | .\" -----------------------------------------------------------------
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| 28 | .\" * MAIN CONTENT STARTS HERE *
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| 29 | .\" -----------------------------------------------------------------
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| 30 | .SH "NAME"
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| 31 | vfs_aio_linux \- implement async I/O in Samba vfs using Linux kernel aio calls
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| 32 | .SH "SYNOPSIS"
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| 33 | .HP \w'\ 'u
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| 34 | vfs objects = aio_linux
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| 35 | .SH "DESCRIPTION"
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| 36 | .PP
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| 37 | This VFS module is part of the
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| 38 | \fBsamba\fR(7)
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| 39 | suite\&.
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| 40 | .PP
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| 41 | The
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| 42 | aio_linux
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| 43 | 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\&.
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| 44 | .PP
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| 45 | 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\&.
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| 46 | .PP
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| 47 | Note that the smb\&.conf parameters
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| 48 | aio read size
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| 49 | and
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| 50 | aio write size
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| 51 | must also be set appropriately for this module to be active\&.
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| 52 | .PP
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| 53 | 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\&.
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| 54 | .SH "EXAMPLES"
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| 55 | .PP
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| 56 | Straight forward use:
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| 57 | .sp
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| 58 | .if n \{\
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| 59 | .RS 4
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| 60 | .\}
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| 61 | .nf
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| 62 | \fI[cooldata]\fR
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| 63 | \m[blue]\fBpath = /data/ice\fR\m[]
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| 64 | \m[blue]\fBaio read size = 1024\fR\m[]
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| 65 | \m[blue]\fBaio write size = 1024\fR\m[]
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| 66 | \m[blue]\fBvfs objects = aio_linux\fR\m[]
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| 67 | .fi
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| 68 | .if n \{\
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| 69 | .RE
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| 70 | .\}
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| 71 | .SH "OPTIONS"
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| 72 | .PP
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| 73 | aio_linux:aio num events = INTEGER
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| 74 | .RS 4
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| 75 | Set the maximum size of the event queue that is used to limit outstanding IO requests\&.
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| 76 | .sp
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| 77 | By default this is set to 128\&.
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| 78 | .RE
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| 79 | .SH "VERSION"
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| 80 | .PP
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| 81 | This man page is correct for version 4\&.0 of the Samba suite\&.
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| 82 | .SH "AUTHOR"
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| 83 | .PP
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| 84 | 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\&.
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