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<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter�29.�High Availability</title><link rel="stylesheet" href="samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.64.1"><link rel="home" href="index.html" title="The Official Samba-3 HOWTO and Reference Guide"><link rel="up" href="optional.html" title="Part�III.�Advanced Configuration"><link rel="previous" href="Backup.html" title="Chapter�28.�Backup Techniques"><link rel="next" href="migration.html" title="Part�IV.�Migration and Updating"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter�29.�High Availability</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="Backup.html">Prev</a>�</td><th width="60%" align="center">Part�III.�Advanced Configuration</th><td width="20%" align="right">�<a accesskey="n" href="migration.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="SambaHA"></a>Chapter�29.�High Availability</h2></div><div><div class="author"><h3 class="author"><span class="firstname">John</span> <span class="othername">H.</span> <span class="surname">Terpstra</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><tt class="email"><<a href="mailto:jht@samba.org">jht@samba.org</a>></tt></p></div></div></div></div><div><div class="author"><h3 class="author"><span class="firstname">Jeremy</span> <span class="surname">Allison</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><tt class="email"><<a href="mailto:jra@samba.org">jra@samba.org</a>></tt></p></div></div></div></div></div><div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="SambaHA.html#id2588793">Features and Benefits</a></span></dt><dt><span class="sect1"><a href="SambaHA.html#id2588851">Technical Discussion</a></span></dt><dd><dl><dt><span class="sect2"><a href="SambaHA.html#id2588865">The Ultimate Goal</a></span></dt><dt><span class="sect2"><a href="SambaHA.html#id2588945">Why Is This So Hard?</a></span></dt><dt><span class="sect2"><a href="SambaHA.html#id2589320">A Simple Solution</a></span></dt><dt><span class="sect2"><a href="SambaHA.html#id2589359">High Availability Server Products</a></span></dt><dt><span class="sect2"><a href="SambaHA.html#id2589416">MS-DFS: The Poor Man's Cluster</a></span></dt><dt><span class="sect2"><a href="SambaHA.html#id2589453">Conclusions</a></span></dt></dl></dd></dl></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2588793"></a>Features and Benefits</h2></div></div><div></div></div><p>
1
<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter�30.�High Availability</title><link rel="stylesheet" href="samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.66.1"><link rel="start" href="index.html" title="The Official Samba-3 HOWTO and Reference Guide"><link rel="up" href="optional.html" title="Part�III.�Advanced Configuration"><link rel="prev" href="Backup.html" title="Chapter�29.�Backup Techniques"><link rel="next" href="largefile.html" title="Chapter�31.�Handling Large Directories"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter�30.�High Availability</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="Backup.html">Prev</a>�</td><th width="60%" align="center">Part�III.�Advanced Configuration</th><td width="20%" align="right">�<a accesskey="n" href="largefile.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="SambaHA"></a>Chapter�30.�High Availability</h2></div><div><div class="author"><h3 class="author"><span class="firstname">John</span> <span class="othername">H.</span> <span class="surname">Terpstra</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><tt class="email"><<a href="mailto:jht@samba.org">jht@samba.org</a>></tt></p></div></div></div></div><div><div class="author"><h3 class="author"><span class="firstname">Jeremy</span> <span class="surname">Allison</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><tt class="email"><<a href="mailto:jra@samba.org">jra@samba.org</a>></tt></p></div></div></div></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="SambaHA.html#id2609910">Features and Benefits</a></span></dt><dt><span class="sect1"><a href="SambaHA.html#id2609962">Technical Discussion</a></span></dt><dd><dl><dt><span class="sect2"><a href="SambaHA.html#id2609976">The Ultimate Goal</a></span></dt><dt><span class="sect2"><a href="SambaHA.html#id2610056">Why Is This So Hard?</a></span></dt><dt><span class="sect2"><a href="SambaHA.html#id2610430">A Simple Solution</a></span></dt><dt><span class="sect2"><a href="SambaHA.html#id2610469">High Availability Server Products</a></span></dt><dt><span class="sect2"><a href="SambaHA.html#id2610526">MS-DFS: The Poor Man's Cluster</a></span></dt><dt><span class="sect2"><a href="SambaHA.html#id2610563">Conclusions</a></span></dt></dl></dd></dl></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2609910"></a>Features and Benefits</h2></div></div></div><p>
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Network administrators are often concerned about the availability of file and print
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services. Network users are inclined toward intolerance of the services they depend
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on to perform vital task responsibilities.
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rise to the challenge of providing a detailed document that is focused purely on
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presentation of the current state of knowledge and practice in high availability as it
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applies to the deployment of Samba and other CIFS/SMB technologies.
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</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2588851"></a>Technical Discussion</h2></div></div><div></div></div><p>
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</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2609962"></a>Technical Discussion</h2></div></div></div><p>
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The following summary was part of a presentation by Jeremy Allison at the SambaXP 2003
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conference that was held at Goettingen, Germany, in April 2003. Material has been added
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from other sources, but it was Jeremy who inspired the structure that follows.
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</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2588865"></a>The Ultimate Goal</h3></div></div><div></div></div><p>
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</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2609976"></a>The Ultimate Goal</h3></div></div></div><p>
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All clustering technologies aim to achieve one or more of the following:
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</p><div class="itemizedlist"><ul type="disc"><li><p>Obtain the maximum affordable computational power.</p></li><li><p>Obtain faster program execution.</p></li><li><p>Deliver unstoppable services.</p></li><li><p>Avert points of failure.</p></li><li><p>Exact most effective utilization of resources.</p></li></ul></div><p>
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A clustered file server ideally has the following properties:
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</p><div class="itemizedlist"><ul type="disc"><li><p>All clients can connect transparently to any server.</p></li><li><p>A server can fail and clients are transparently reconnected to another server.</p></li><li><p>All servers server out the same set of files.</p></li><li><p>All file changes are immediately seen on all servers.</p><div class="itemizedlist"><ul type="circle"><li><p>Requires a distributed file system.</p></li></ul></div></li><li><p>Infinite ability to scale by adding more servers or disks.</p></li></ul></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2588945"></a>Why Is This So Hard?</h3></div></div><div></div></div><p>
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</p><div class="itemizedlist"><ul type="disc"><li><p>All clients can connect transparently to any server.</p></li><li><p>A server can fail and clients are transparently reconnected to another server.</p></li><li><p>All servers server out the same set of files.</p></li><li><p>All file changes are immediately seen on all servers.</p><div class="itemizedlist"><ul type="circle"><li><p>Requires a distributed file system.</p></li></ul></div></li><li><p>Infinite ability to scale by adding more servers or disks.</p></li></ul></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2610056"></a>Why Is This So Hard?</h3></div></div></div><p>
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In short, the problem is one of <span class="emphasis"><em>state</em></span>.
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</p><div class="itemizedlist"><ul type="disc"><li><p>
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All TCP/IP connections are dependent on state information.
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Servers keep state information about client connections.
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</p><div class="itemizedlist"><ul type="circle"><li><p>CIFS/SMB involves a lot of state.</p></li><li><p>Every file open must be compared with other file opens
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to check share modes.</p></li></ul></div><p>
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</p></li></ul></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2589023"></a>The Front-End Challenge</h4></div></div><div></div></div><p>
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</p></li></ul></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2610134"></a>The Front-End Challenge</h4></div></div></div><p>
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To make it possible for a cluster of file servers to appear as a single server that has one
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name and one IP address, the incoming TCP data streams from clients must be processed by the
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front end virtual server. This server must de-multiplex the incoming packets at the SMB protocol
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Conceptually speaking, all other servers would then provide only file services. This is a simpler
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problem to concentrate on.
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</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2589056"></a>De-multiplexing SMB Requests</h4></div></div><div></div></div><p>
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</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2610167"></a>De-multiplexing SMB Requests</h4></div></div></div><p>
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De-multiplexing of SMB requests requires knowledge of SMB state information,
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all of which must be held by the front-end <span class="emphasis"><em>virtual</em></span> server.
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This is a perplexing and complicated problem to solve.
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One possibility is to start by exposing the server pool to clients directly.
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This could eliminate the de-multiplexing step.
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</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2589093"></a>The Distributed File System Challenge</h4></div></div><div></div></div><p>
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<a class="indexterm" name="id2589101"></a>
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</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2610203"></a>The Distributed File System Challenge</h4></div></div></div><p>
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<a class="indexterm" name="id2610211"></a>
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There exists many distributed file systems for UNIX and Linux.
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Many could be adopted to backend our cluster, so long as awareness of SMB
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semantics is kept in mind (share modes, locking and oplock issues in particular).
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Common free distributed file systems include:
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<a class="indexterm" name="id2589116"></a>
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<a class="indexterm" name="id2589123"></a>
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<a class="indexterm" name="id2589130"></a>
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<a class="indexterm" name="id2589136"></a>
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<a class="indexterm" name="id2610227"></a>
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<a class="indexterm" name="id2610234"></a>
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<a class="indexterm" name="id2610240"></a>
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<a class="indexterm" name="id2610247"></a>
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</p><div class="itemizedlist"><ul type="disc"><li><p>NFS</p></li><li><p>AFS</p></li><li><p>OpenGFS</p></li><li><p>Lustre</p></li></ul></div><p>
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The server pool (cluster) can use any distributed file system backend if all SMB
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semantics are performed within this pool.
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</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2589172"></a>Restrictive Constraints on Distributed File Systems</h4></div></div><div></div></div><p>
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</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2610282"></a>Restrictive Constraints on Distributed File Systems</h4></div></div></div><p>
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Where a clustered server provides purely SMB services, oplock handling
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may be done within the server pool without imposing a need for this to
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be passed to the backend file system pool.
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sorely noted by users of Microsoft Windows clients.
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Last, all state information must be shared across the server pool.
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</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2589200"></a>Server Pool Communications</h4></div></div><div></div></div><p>
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</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2610310"></a>Server Pool Communications</h4></div></div></div><p>
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Most backend file systems support POSIX file semantics. This makes it difficult
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to push SMB semantics back into the file system. POSIX locks have different properties
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and semantics from SMB locks.
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All <span><b class="command">smbd</b></span> processes in the server pool must of necessity communicate
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very quickly. For this, the current <i class="parameter"><tt>tdb</tt></i> file structure that Samba
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uses is not suitable for use across a network. Clustered <span><b class="command">smbd</b></span>'s must use something else.
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</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2589238"></a>Server Pool Communications Demands</h4></div></div><div></div></div><p>
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</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2610349"></a>Server Pool Communications Demands</h4></div></div></div><p>
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High speed inter-server communications in the server pool is a design prerequisite
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for a fully functional system. Possibilities for this include:
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</p><div class="itemizedlist"><ul type="disc"><li><p>
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</p></li></ul></div><p>
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We have yet to identify metrics for performance demands to enable this to happen
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</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2589277"></a>Required Modifications to Samba</h4></div></div><div></div></div><p>
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</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2610387"></a>Required Modifications to Samba</h4></div></div></div><p>
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Samba needs to be significantly modified to work with a high-speed server inter-connect
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system to permit transparent fail-over clustering.
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Should this be implemented using a point-to-point lock manager, or can this
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be done using multicast techniques?
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</p></li></ul></div></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2589320"></a>A Simple Solution</h3></div></div><div></div></div><p>
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</p></li></ul></div></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2610430"></a>A Simple Solution</h3></div></div></div><p>
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Allowing fail-over servers to handle different functions within the exported file system
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removes the problem of requiring a distributed locking protocol.
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The <span class="emphasis"><em>virtual server</em></span> is still needed to redirect requests to backend
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servers. Backend file space integrity is the responsibility of the administrator.
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</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2589359"></a>High Availability Server Products</h3></div></div><div></div></div><p>
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</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2610469"></a>High Availability Server Products</h3></div></div></div><p>
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Fail-over servers must communicate in order to handle resource fail-over. This is essential
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for high availability services. The use of a dedicated heartbeat is a common technique to
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introduce some intelligence into the fail-over process. This is often done over a dedicated
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link (LAN or serial).
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<a class="indexterm" name="id2589375"></a>
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<a class="indexterm" name="id2610486"></a>
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Many fail-over solutions (like Red Hat Cluster Manager, as well as Microsoft Wolfpack)
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can use a shared SCSI of Fiber Channel disk storage array for fail-over communication.
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Information regarding Red Hat high availability solutions for Samba may be obtained from:
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Front-end server complexity remains a challenge for high availability as it needs to deal
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gracefully with backend failures, while at the same time it needs to provide continuity of service
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to all network clients.
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</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2589416"></a>MS-DFS: The Poor Man's Cluster</h3></div></div><div></div></div><p>
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<a class="indexterm" name="id2589424"></a>
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<a class="indexterm" name="id2589431"></a>
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</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2610526"></a>MS-DFS: The Poor Man's Cluster</h3></div></div></div><p>
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<a class="indexterm" name="id2610534"></a>
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<a class="indexterm" name="id2610541"></a>
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MS-DFS links can be used to redirect clients to disparate backend servers. This pushes
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complexity back to the network client, something already included by Microsoft.
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MS-DFS creates the illusion of a simple, continuous file system name space, that even
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Above all, at the cost of complexity of management, a distributed (pseudo-cluster) can
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be created using existing Samba functionality.
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</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2589453"></a>Conclusions</h3></div></div><div></div></div><div class="itemizedlist"><ul type="disc"><li><p>Transparent SMB clustering is hard to do!</p></li><li><p>Client fail-over is the best we can do today.</p></li><li><p>Much more work is needed before a practical and manageable high
188
availability transparent cluster solution will be possible.</p></li><li><p>MS-DFS can be used to create the illusion of a single transparent cluster.</p></li></ul></div></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="Backup.html">Prev</a>�</td><td width="20%" align="center"><a accesskey="u" href="optional.html">Up</a></td><td width="40%" align="right">�<a accesskey="n" href="migration.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter�28.�Backup Techniques�</td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top">�Part�IV.�Migration and Updating</td></tr></table></div></body></html>
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</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2610563"></a>Conclusions</h3></div></div></div><div class="itemizedlist"><ul type="disc"><li><p>Transparent SMB clustering is hard to do!</p></li><li><p>Client fail-over is the best we can do today.</p></li><li><p>Much more work is needed before a practical and manageable high
188
availability transparent cluster solution will be possible.</p></li><li><p>MS-DFS can be used to create the illusion of a single transparent cluster.</p></li></ul></div></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="Backup.html">Prev</a>�</td><td width="20%" align="center"><a accesskey="u" href="optional.html">Up</a></td><td width="40%" align="right">�<a accesskey="n" href="largefile.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter�29.�Backup Techniques�</td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top">�Chapter�31.�Handling Large Directories</td></tr></table></div></body></html>
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