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diff --git a/docs/htmldocs/Samba3-ByExample/HA.html b/docs/htmldocs/Samba3-ByExample/HA.html new file mode 100644 index 0000000000..3522f72ea4 --- /dev/null +++ b/docs/htmldocs/Samba3-ByExample/HA.html @@ -0,0 +1,416 @@ +<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 13. Performance, Reliability, and Availability</title><link rel="stylesheet" href="samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.71.0"><link rel="start" href="index.html" title="Samba-3 by Example"><link rel="up" href="RefSection.html" title="Part III. Reference Section"><link rel="prev" href="DomApps.html" title="Chapter 12. Integrating Additional Services"><link rel="next" href="ch14.html" title="Chapter 14. Samba Support"></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 13. Performance, Reliability, and Availability</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="DomApps.html">Prev</a> </td><th width="60%" align="center">Part III. Reference Section</th><td width="20%" align="right"> <a accesskey="n" href="ch14.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="HA"></a>Chapter 13. Performance, Reliability, and Availability</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="HA.html#id380314">Introduction</a></span></dt><dt><span class="sect1"><a href="HA.html#id380391">Dissection and Discussion</a></span></dt><dt><span class="sect1"><a href="HA.html#id380842">Guidelines for Reliable Samba Operation</a></span></dt><dd><dl><dt><span class="sect2"><a href="HA.html#id380866">Name Resolution</a></span></dt><dt><span class="sect2"><a href="HA.html#id381308">Samba Configuration</a></span></dt><dt><span class="sect2"><a href="HA.html#id381603">Use and Location of BDCs</a></span></dt><dt><span class="sect2"><a href="HA.html#id381671">Use One Consistent Version of MS Windows Client</a></span></dt><dt><span class="sect2"><a href="HA.html#id381688">For Scalability, Use SAN-Based Storage on Samba Servers</a></span></dt><dt><span class="sect2"><a href="HA.html#id381733">Distribute Network Load with MSDFS</a></span></dt><dt><span class="sect2"><a href="HA.html#id381784">Replicate Data to Conserve Peak-Demand Wide-Area Bandwidth</a></span></dt><dt><span class="sect2"><a href="HA.html#id381824">Hardware Problems</a></span></dt><dt><span class="sect2"><a href="HA.html#id381957">Large Directories</a></span></dt></dl></dd><dt><span class="sect1"><a href="HA.html#id382035">Key Points Learned</a></span></dt></dl></div><p> + <a class="indexterm" name="id380277"></a> + <a class="indexterm" name="id380283"></a> + <a class="indexterm" name="id380290"></a> + Well, you have reached one of the last chapters of this book. It is customary to attempt + to wrap up the theme and contents of a book in what is generally regarded as the + chapter that should draw conclusions. This book is a suspense thriller, and since + the plot of the stories told mostly lead you to bigger, better Samba-3 networking + solutions, it is perhaps appropriate to close this book with a few pertinent comments + regarding some of the things everyone can do to deliver a reliable Samba-3 network. + </p><div class="blockquote"><table border="0" width="100%" cellspacing="0" cellpadding="0" class="blockquote" summary="Block quote"><tr><td width="10%" valign="top"> </td><td width="80%" valign="top"><p> + In a world so full of noise, how can the sparrow be heard? + </p></td><td width="10%" valign="top"> </td></tr><tr><td width="10%" valign="top"> </td><td colspan="2" align="right" valign="top">--<span class="attribution">Anonymous</span></td></tr></table></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id380314"></a>Introduction</h2></div></div></div><p> + <a class="indexterm" name="id380322"></a> + The sparrow is a small bird whose sounds are drowned out by the noise of the busy + world it lives in. Likewise, the simple steps that can be taken to improve the + reliability and availability of a Samba network are often drowned out by the volume + of discussions about grandiose Samba clustering designs. This is not intended to + suggest that clustering is not important, because clearly it is. This chapter does not devote + itself to discussion of clustering because each clustering methodology uses its own + custom tools and methods. Only passing comments are offered concerning these methods. + </p><p> + <a class="indexterm" name="id380337"></a> + <a class="indexterm" name="id380343"></a> + <a class="indexterm" name="id380350"></a> +<a href="http://www.google.com/search?hl=en&lr=&ie=ISO-8859-1&q=samba+cluster&btnG=Google+Search" target="_top">A search</a> + for “<span class="quote">samba cluster</span>” produced 71,600 hits. And a search for “<span class="quote">highly available samba</span>” + and “<span class="quote">highly available windows</span>” produced an amazing number of references. + It is clear from the resources on the Internet that Windows file and print services + availability, reliability, and scalability are of vital interest to corporate network users. + </p><p> + <a class="indexterm" name="id380380"></a> + So without further background, you can review a checklist of simple steps that + can be taken to ensure acceptable network performance while keeping costs of ownership + well under control. + </p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id380391"></a>Dissection and Discussion</h2></div></div></div><p> + <a class="indexterm" name="id380399"></a> + <a class="indexterm" name="id380406"></a> + If it is your purpose to get the best mileage out of your Samba servers, there is one rule that + must be obeyed. If you want the best, keep your implementation as simple as possible. You may + well be forced to introduce some complexities, but you should do so only as a last resort. + </p><p> + Simple solutions are likely to be easier to get right than are complex ones. They certainly + make life easier for your successor. Simple implementations can be more readily audited than can + complex ones. + </p><p> + <a class="indexterm" name="id380423"></a> + <a class="indexterm" name="id380430"></a> + Problems reported by users fall into three categories: configurations that do not work, those + that have broken behavior, and poor performance. The term <span class="emphasis"><em>broken behavior</em></span> + means that the function of a particular Samba component appears to work sometimes, but not at + others. The resulting intermittent operation is clearly unacceptable. An example of + <span class="emphasis"><em>broken behavior</em></span> known to many Windows networking users occurs when the + list of Windows machines in MS Explorer changes, sometimes listing machines that are running + and at other times not listing them even though the machines are in use on the network. + </p><p> + <a class="indexterm" name="id380452"></a> + <a class="indexterm" name="id380459"></a> + <a class="indexterm" name="id380466"></a> + <a class="indexterm" name="id380472"></a> + <a class="indexterm" name="id380479"></a> + <a class="indexterm" name="id380486"></a> + A significant number of reports concern problems with the <code class="literal">smbfs</code> file system + driver that is part of the Linux kernel, not part of Samba. Users continue to interpret that + <code class="literal">smbfs</code> is part of Samba, simply because Samba includes the front-end tools + that are used to manage <code class="literal">smbfs</code>-based file service connections. So, just + for the record, the tools <code class="literal">smbmnt</code>, <code class="literal">smbmount</code>, + <code class="literal">smbumount</code>, and <code class="literal">smbumnt</code> are front-end + facilities to core drivers that are supplied as part of the Linux kernel. These tools share a + common infrastructure with some Samba components, but they are not maintained as part of + Samba and are really foreign to it. + </p><p> + <a class="indexterm" name="id380542"></a> + The new project, <code class="literal">cifsfs</code>, is destined to replace <code class="literal">smbfs</code>. + It, too, is not part of Samba, even though one of the Samba Team members is a prime mover in + this project. + </p><p> + Table 13.1 lists typical causes of: + </p><div class="itemizedlist"><ul type="disc"><li><p>Not Working (NW)</p></li><li><p>Broken Behavior (BB)</p></li><li><p>Poor Performance (PP)</p></li></ul></div><div class="table"><a name="ProbList"></a><p class="title"><b>Table 13.1. Effect of Common Problems</b></p><div class="table-contents"><table summary="Effect of Common Problems" border="1"><colgroup><col align="left"><col align="center"><col align="center"><col align="center"></colgroup><thead><tr><th align="left"><p>Problem</p></th><th align="center"><p>NW</p></th><th align="center"><p>BB</p></th><th align="center"><p>PP</p></th></tr></thead><tbody><tr><td align="left"><p>File locking</p></td><td align="center"><p>-</p></td><td align="center"><p>X</p></td><td align="center"><p>-</p></td></tr><tr><td align="left"><p>Hardware problems</p></td><td align="center"><p>X</p></td><td align="center"><p>X</p></td><td align="center"><p>X</p></td></tr><tr><td align="left"><p>Incorrect authentication</p></td><td align="center"><p>X</p></td><td align="center"><p>X</p></td><td align="center"><p>-</p></td></tr><tr><td align="left"><p>Incorrect configuration</p></td><td align="center"><p>X</p></td><td align="center"><p>X</p></td><td align="center"><p>X</p></td></tr><tr><td align="left"><p>LDAP problems</p></td><td align="center"><p>X</p></td><td align="center"><p>X</p></td><td align="center"><p>-</p></td></tr><tr><td align="left"><p>Name resolution</p></td><td align="center"><p>X</p></td><td align="center"><p>X</p></td><td align="center"><p>X</p></td></tr><tr><td align="left"><p>Printing problems</p></td><td align="center"><p>X</p></td><td align="center"><p>X</p></td><td align="center"><p>-</p></td></tr><tr><td align="left"><p>Slow file transfer</p></td><td align="center"><p>-</p></td><td align="center"><p>-</p></td><td align="center"><p>X</p></td></tr><tr><td align="left"><p>Winbind problems</p></td><td align="center"><p>X</p></td><td align="center"><p>X</p></td><td align="center"><p>-</p></td></tr></tbody></table></div></div><br class="table-break"><p> + <a class="indexterm" name="id380831"></a> + It is obvious to all that the first requirement (as a matter of network hygiene) is to eliminate + problems that affect basic network operation. This book has provided sufficient working examples + to help you to avoid all these problems. + </p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id380842"></a>Guidelines for Reliable Samba Operation</h2></div></div></div><p> + <a class="indexterm" name="id380850"></a> + <a class="indexterm" name="id380856"></a> + Your objective is to provide a network that works correctly, can grow at all times, is resilient + at times of extreme demand, and can scale to meet future needs. The following subject areas provide + pointers that can help you today. + </p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id380866"></a>Name Resolution</h3></div></div></div><p> + There are three basic current problem areas: bad hostnames, routed networks, and network collisions. + These are covered in the following discussion. + </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id380877"></a>Bad Hostnames</h4></div></div></div><p> + <a class="indexterm" name="id380884"></a> + <a class="indexterm" name="id380894"></a> + <a class="indexterm" name="id380900"></a> + <a class="indexterm" name="id380907"></a> + <a class="indexterm" name="id380914"></a> + When configured as a DHCP client, a number of Linux distributions set the system hostname + to <code class="constant">localhost</code>. If the parameter <em class="parameter"><code>netbios name</code></em> is not + specified to something other than <code class="constant">localhost</code>, the Samba server appears + in the Windows Explorer as <code class="constant">LOCALHOST</code>. Moreover, the entry in the <code class="filename">/etc/hosts</code> + on the Linux server points to IP address <code class="constant">127.0.0.1</code>. This means that + when the Windows client obtains the IP address of the Samba server called <code class="constant">LOCALHOST</code>, + it obtains the IP address <code class="constant">127.0.0.1</code> and then proceeds to attempt to + set up a NetBIOS over TCP/IP connection to it. This cannot work, because that IP address is + the local Windows machine itself. Hostnames must be valid for Windows networking to function + correctly. + </p><p> + <a class="indexterm" name="id380963"></a> + A few sites have tried to name Windows clients and Samba servers with a name that begins + with the digits 1-9. This does not work either because it may result in the client or + server attempting to use that name as an IP address. + </p><p> + <a class="indexterm" name="id380975"></a> + <a class="indexterm" name="id380984"></a> + A Samba server called <code class="constant">FRED</code> in a NetBIOS domain called <code class="constant">COLLISION</code> + in a network environment that is part of the fully-qualified Internet domain namespace known + as <code class="constant">parrots.com</code>, results in DNS name lookups for <code class="constant">fred.parrots.com</code> + and <code class="constant">collision.parrots.com</code>. It is therefore a mistake to name the domain + (workgroup) <code class="constant">collision.parrots.com</code>, since this results in DNS lookup + attempts to resolve <code class="constant">fred.parrots.com.parrots.com</code>, which most likely + fails given that you probably do not have this in your DNS namespace. + </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p> + <a class="indexterm" name="id381024"></a> + <a class="indexterm" name="id381033"></a> + <a class="indexterm" name="id381040"></a> + An Active Directory realm called <code class="constant">collision.parrots.com</code> is perfectly okay, + although it too must be capable of being resolved via DNS, something that functions correctly + if Windows 200x ADS has been properly installed and configured. + </p></div></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id381054"></a>Routed Networks</h4></div></div></div><p> + <a class="indexterm" name="id381062"></a> + <a class="indexterm" name="id381069"></a> + <a class="indexterm" name="id381078"></a> + NetBIOS networks (Windows networking with NetBIOS over TCP/IP enabled) makes extensive use + of UDP-based broadcast traffic, as you saw during the exercises in <a href="primer.html" title="Chapter 16. Networking Primer">???</a>. + </p><p> + <a class="indexterm" name="id381096"></a> + <a class="indexterm" name="id381103"></a> + <a class="indexterm" name="id381110"></a> + UDP broadcast traffic is not forwarded by routers. This means that NetBIOS broadcast-based + networking cannot function across routed networks (i.e., multi-subnet networks) unless + special provisions are made: + </p><div class="itemizedlist"><ul type="disc"><li><p> + <a class="indexterm" name="id381125"></a> + <a class="indexterm" name="id381132"></a> + <a class="indexterm" name="id381139"></a> + Either install on every Windows client an LMHOSTS file (located in the directory + <code class="filename">C:\windows\system32\drivers\etc</code>). It is also necessary to + add to the Samba server <code class="filename">smb.conf</code> file the parameters <em class="parameter"><code>remote announce</code></em> + and <em class="parameter"><code>remote browse sync</code></em>. For more information, refer to the online + manual page for the <code class="filename">smb.conf</code> file. + </p></li><li><p> + <a class="indexterm" name="id381182"></a> + Or configure Samba as a WINS server, and configure all network clients to use that + WINS server in their TCP/IP configuration. + </p></li></ul></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p> + <a class="indexterm" name="id381197"></a> + <a class="indexterm" name="id381207"></a> + The use of DNS is not an acceptable substitute for WINS. DNS does not store specific + information regarding NetBIOS networking particulars that get stored in the WINS + name resolution database and that Windows clients require and depend on. + </p></div></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id381218"></a>Network Collisions</h4></div></div></div><p> + <a class="indexterm" name="id381225"></a> + <a class="indexterm" name="id381234"></a> + <a class="indexterm" name="id381244"></a> + <a class="indexterm" name="id381250"></a> + Excessive network activity causes NetBIOS network timeouts. Timeouts may result in + blue screen of death (BSOD) experiences. High collision rates may be caused by excessive + UDP broadcast activity, by defective networking hardware, or through excessive network + loads (another way of saying that the network is poorly designed). + </p><p> + The use of WINS is highly recommended to reduce network broadcast traffic, as outlined + in <a href="primer.html" title="Chapter 16. Networking Primer">???</a>. + </p><p> + <a class="indexterm" name="id381276"></a> + <a class="indexterm" name="id381282"></a> + <a class="indexterm" name="id381289"></a> + Under no circumstances should the facility be supported by many routers, known as <code class="constant">NetBIOS + forwarding</code>, unless you know exactly what you are doing. Inappropriate use of this + facility can result in UDP broadcast storms. In one case in 1999, a university network became + unusable due to NetBIOS forwarding being enabled on all routers. The problem was discovered during performance + testing of a Samba server. The maximum throughput on a 100-Base-T (100 MB/sec) network was + less than 15 KB/sec. After the NetBIOS forwarding was turned off, file transfer performance + immediately returned to 11 MB/sec. + </p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id381308"></a>Samba Configuration</h3></div></div></div><p> + As a general rule, the contents of the <code class="filename">smb.conf</code> file should be kept as simple as possible. + No parameter should be specified unless you know it is essential to operation. + </p><p> + <a class="indexterm" name="id381326"></a> + <a class="indexterm" name="id381333"></a> + <a class="indexterm" name="id381340"></a> + Many UNIX administrators like to fully document the settings in the <code class="filename">smb.conf</code> file. This is a + bad idea because it adds content to the file. The <code class="filename">smb.conf</code> file is re-read by every <code class="literal">smbd</code> + process every time the file timestamp changes (or, on systems where this does not work, every 20 seconds or so). + </p><p> + As the size of the <code class="filename">smb.conf</code> file grows, the risk of introducing parsing errors also increases. + It is recommended to keep a fully documented <code class="filename">smb.conf</code> file on hand, and then to operate Samba only + with an optimized file. + </p><p><a class="indexterm" name="id381386"></a> + The preferred way to maintain a documented file is to call it something like <code class="filename">smb.conf.master</code>. + You can generate the optimized file by executing: +</p><pre class="screen"> +<code class="prompt">root# </code> testparm -s smb.conf.master > smb.conf +</pre><p> + You should carefully observe all warnings issued. It is also a good practice to execute the following + command to confirm correct interpretation of the <code class="filename">smb.conf</code> file contents: +</p><pre class="screen"> +<code class="prompt">root# </code> testparm +Load smb config files from /etc/samba/smb.conf +Can't find include file /etc/samba/machine. +Processing section "[homes]" +Processing section "[print$]" +Processing section "[netlogon]" +Processing section "[Profiles]" +Processing section "[printers]" +Processing section "[media]" +Processing section "[data]" +Processing section "[cdr]" +Processing section "[apps]" +Loaded services file OK. +'winbind separator = +' might cause problems with group membership. +Server role: ROLE_DOMAIN_PDC +Press enter to see a dump of your service definitions +</pre><p> + <a class="indexterm" name="id381437"></a> + You now, of course, press the enter key to complete the command, or else abort it by pressing Ctrl-C. + The important thing to note is the noted Server role, as well as warning messages. Noted configuration + conflicts must be remedied before proceeding. For example, the following error message represents a + common fatal problem: +</p><pre class="screen"> +ERROR: both 'wins support = true' and 'wins server = <server list>' +cannot be set in the smb.conf file. nmbd will abort with this setting. +</pre><p> + </p><p> + <a class="indexterm" name="id381458"></a> + <a class="indexterm" name="id381465"></a> + <a class="indexterm" name="id381472"></a> + There are two parameters that can cause severe network performance degradation: <em class="parameter"><code>socket options</code></em> + and <em class="parameter"><code>socket address</code></em>. The <em class="parameter"><code>socket options</code></em> parameter was often necessary + when Samba was used with the Linux 2.2.x kernels. Later kernels are largely self-tuning and seldom benefit from + this parameter being set. Do not use either parameter unless it has been proven necessary to use them. + </p><p> + <a class="indexterm" name="id381503"></a> + <a class="indexterm" name="id381510"></a> + <a class="indexterm" name="id381516"></a> + <a class="indexterm" name="id381523"></a> + Another <code class="filename">smb.conf</code> parameter that may cause severe network performance degradation is the + <em class="parameter"><code>strict sync</code></em> parameter. Do not use this at all. There is no good reason + to use this with any modern Windows client. The <em class="parameter"><code>strict sync</code></em> is often + used with the <em class="parameter"><code>sync always</code></em> parameter. This, too, can severely + degrade network performance, so do not set it; if you must, do so with caution. + </p><p> + <a class="indexterm" name="id381562"></a> + <a class="indexterm" name="id381569"></a> + <a class="indexterm" name="id381576"></a> + <a class="indexterm" name="id381582"></a> + Finally, many network administrators deliberately disable opportunistic locking support. While this + does not degrade Samba performance, it significantly degrades Windows client performance because + this disables local file caching on Windows clients and forces every file read and written to + invoke a network read or write call. If for any reason you must disable oplocks (opportunistic locking) + support, do so only on the share on which it is required. That way, all other shares can provide + oplock support for operations that are tolerant of it. See <a href="appendix.html#ch12dblck" title="Shared Data Integrity">???</a> for more + information. + </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id381603"></a>Use and Location of BDCs</h3></div></div></div><p> + <a class="indexterm" name="id381611"></a> + <a class="indexterm" name="id381617"></a> + <a class="indexterm" name="id381624"></a> + <a class="indexterm" name="id381631"></a> + <a class="indexterm" name="id381638"></a> + On a network segment where there is a PDC and a BDC, the BDC carries the bulk of the network logon + processing. If the BDC is a heavily loaded server, the PDC carries a greater proportion of + authentication and logon processing. When a sole BDC on a routed network segment gets heavily + loaded, it is possible that network logon requests and authentication requests may be directed + to a BDC on a distant network segment. This significantly hinders WAN operations + and is undesirable. + </p><p> + <a class="indexterm" name="id381652"></a> + <a class="indexterm" name="id381659"></a> + As a general guide, instead of adding domain member servers to a network, you would be better advised + to add BDCs until there are fewer than 30 Windows clients per BDC. Beyond that ratio, you should add + domain member servers. This practice ensures that there are always sufficient domain controllers + to handle logon requests and authentication traffic. + </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id381671"></a>Use One Consistent Version of MS Windows Client</h3></div></div></div><p> + Every network client has its own peculiarities. From a management perspective, it is easier to deal + with one version of MS Windows that is maintained to a consistent update level than it is to deal + with a mixture of clients. + </p><p> + On a number of occasions, particular Microsoft service pack updates of a Windows server or client + have necessitated special handling from the Samba server end. If you want to remain sane, keep you + client workstation configurations consistent. + </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id381688"></a>For Scalability, Use SAN-Based Storage on Samba Servers</h3></div></div></div><p> + <a class="indexterm" name="id381696"></a> + <a class="indexterm" name="id381703"></a> + Many SAN-based storage systems permit more than one server to share a common data store. + Use of a shared SAN data store means that you do not need to use time- and resource-hungry data + synchronization techniques. + </p><p> + <a class="indexterm" name="id381715"></a> + <a class="indexterm" name="id381722"></a> + The use of a collection of relatively low-cost front-end Samba servers that are coupled to + a shared backend SAN data store permits load distribution while containing costs below that + of installing and managing a complex clustering facility. + </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id381733"></a>Distribute Network Load with MSDFS</h3></div></div></div><p> + <a class="indexterm" name="id381741"></a> + <a class="indexterm" name="id381748"></a> + Microsoft DFS (distributed file system) technology has been implemented in Samba. MSDFS permits + data to be accessed from a single share and yet to actually be distributed across multiple actual + servers. Refer to <span class="emphasis"><em>TOSHARG2</em></span>, Chapter 19, for information regarding + implementation of an MSDFS installation. + </p><p> + <a class="indexterm" name="id381764"></a> + <a class="indexterm" name="id381773"></a> + The combination of multiple backend servers together with a front-end server and use of MSDFS + can achieve almost the same as you would obtain with a clustered Samba server. + </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id381784"></a>Replicate Data to Conserve Peak-Demand Wide-Area Bandwidth</h3></div></div></div><p> + <a class="indexterm" name="id381792"></a> + <a class="indexterm" name="id381798"></a> + <a class="indexterm" name="id381805"></a> + Consider using <code class="literal">rsync</code> to replicate data across the WAN during times + of low utilization. Users can then access the replicated data store rather than needing to do so + across the WAN. This works best for read-only data, but with careful planning can be + implemented so that modified files get replicated back to the point of origin. Be careful with your + implementation if you choose to permit modification and return replication of the modified file; + otherwise, you may inadvertently overwrite important data. + </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id381824"></a>Hardware Problems</h3></div></div></div><p> + <a class="indexterm" name="id381832"></a> + <a class="indexterm" name="id381839"></a> + <a class="indexterm" name="id381846"></a> + <a class="indexterm" name="id381853"></a> + <a class="indexterm" name="id381862"></a> + <a class="indexterm" name="id381871"></a> + Networking hardware prices have fallen sharply over the past 5 years. A surprising number + of Samba networking problems over this time have been traced to defective network interface + cards (NICs) or defective HUBs, switches, and cables. + </p><p> + <a class="indexterm" name="id381886"></a> + Not surprising is the fact that network administrators do not like to be shown to have made + a bad decision. Money saved in buying low-cost hardware may result in high costs incurred + in corrective action. + </p><p> + <a class="indexterm" name="id381897"></a> + <a class="indexterm" name="id381904"></a> + <a class="indexterm" name="id381911"></a> + <a class="indexterm" name="id381918"></a> + <a class="indexterm" name="id381925"></a> + Defective NICs, HUBs, and switches may appear as intermittent network access problems, intermittent + or persistent data corruption, slow network throughput, low performance, or even as BSOD + problems with MS Windows clients. In one case, a company updated several workstations with newer, faster + Windows client machines that triggered problems during logon as well as data integrity problems on + an older PC that was unaffected so long as the new machines were kept shut down. + </p><p> + Defective hardware problems may take patience and persistence before the real cause can be discovered. + </p><p> + <a class="indexterm" name="id381943"></a> + Networking hardware defects can significantly impact perceived Samba performance, but defective + RAID controllers as well as SCSI and IDE hard disk controllers have also been known to impair Samba server + operations. One business came to this realization only after replacing a Samba installation with MS + Windows Server 2000 running on the same hardware. The root of the problem completely eluded the network + administrator until the entire server was replaced. While you may well think that this would never + happen to you, experience shows that given the right (unfortunate) circumstances, this can happen to anyone. + </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id381957"></a>Large Directories</h3></div></div></div><p> + There exist applications that create or manage directories containing many thousands of files. Such + applications typically generate many small files (less than 100 KB). At the best of times, under UNIX, + listing of the files in a directory that contains many files is slow. By default, Windows NT, 200x, + and XP Pro cause network file system directory lookups on a Samba server to be performed for both + the case preserving file name as well as for the mangled (8.3) file name. This incurs a huge overhead + on the Samba server that may slow down the system dramatically. + </p><p> + In an extreme case, the performance impact was dramatic. File transfer from the Samba server to a Windows + XP Professional workstation over 1 Gigabit Ethernet for 250-500 KB files was measured at approximately + 30 MB/sec. But when tranferring a directory containing 120,000 files, all from 50KB to 60KB in size, the + transfer rate to the same workstation was measured at approximately 1.5 KB/sec. The net transfer was + on the order of a factor of 20-fold slower. + </p><p> + The symptoms that will be observed on the Samba server when a large directory is accessed will be that + aggregate I/O (typically blocks read) will be relatively low, yet the wait I/O times will be incredibly + long while at the same time the read queue is large. Close observation will show that the hard drive + that the file system is on will be thrashing wildly. + </p><p> + Samba-3.0.12 and later, includes new code that radically improves Samba perfomance. The secret to this is + really in the <a class="indexterm" name="id381988"></a>case sensitive = True line. This tells smbd never to scan + for case-insensitive versions of names. So if an application asks for a file called <code class="filename">FOO</code>, + and it can not be found by a simple stat call, then smbd will return "file not found" immediately without + scanning the containing directory for a version of a different case. + </p><p> + Canonicalize all the files in the directory to have one case, upper or lower - either will do. Then set up + a new custom share for the application as follows: + </p><pre class="screen"> + [bigshare] + path = /data/xrayfiles/neurosurgeons/ + read only = no + case sensitive = True + default case = upper + preserve case = no + short preserve case = no + </pre><p> + </p><p> + All files and directories under the <em class="parameter"><code>path</code></em> directory must be in the same case + as specified in the <code class="filename">smb.conf</code> stanza. This means that smbd will not be able to find lower case + filenames with these settings. Note, this is done on a per-share basis. + </p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id382035"></a>Key Points Learned</h2></div></div></div><p> + This chapter has touched in broad sweeps on a number of simple steps that can be taken + to ensure that your Samba network is resilient, scalable, and reliable, and that it + performs well. + </p><p> + Always keep in mind that someone is responsible to maintain and manage your design. + In the long term, that may not be you. Spare a thought for your successor and give him or + her an even break. + </p><p> + <a class="indexterm" name="id382053"></a> + Last, but not least, you should not only keep the network design simple, but also be sure it is + well documented. This book may serve as your pattern for documenting every + aspect of your design, its implementation, and particularly the objects and assumptions + that underlie it. + </p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="DomApps.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="RefSection.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch14.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 12. Integrating Additional Services </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 14. Samba Support</td></tr></table></div></body></html> |