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1<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 V1.74.0"><link rel="home" 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#id2618959">Introduction</a></span></dt><dt><span class="sect1"><a href="HA.html#id2619057">Dissection and Discussion</a></span></dt><dt><span class="sect1"><a href="HA.html#id2619530">Guidelines for Reliable Samba Operation</a></span></dt><dd><dl><dt><span class="sect2"><a href="HA.html#id2619557">Name Resolution</a></span></dt><dt><span class="sect2"><a href="HA.html#id2620033">Samba Configuration</a></span></dt><dt><span class="sect2"><a href="HA.html#id2620360">Use and Location of BDCs</a></span></dt><dt><span class="sect2"><a href="HA.html#id2620435">Use One Consistent Version of MS Windows Client</a></span></dt><dt><span class="sect2"><a href="HA.html#id2620457">For Scalability, Use SAN-Based Storage on Samba Servers</a></span></dt><dt><span class="sect2"><a href="HA.html#id2620507">Distribute Network Load with MSDFS</a></span></dt><dt><span class="sect2"><a href="HA.html#id2620562">Replicate Data to Conserve Peak-Demand Wide-Area Bandwidth</a></span></dt><dt><span class="sect2"><a href="HA.html#id2620607">Hardware Problems</a></span></dt><dt><span class="sect2"><a href="HA.html#id2620755">Large Directories</a></span></dt></dl></dd><dt><span class="sect1"><a href="HA.html#id2620859">Key Points Learned</a></span></dt></dl></div><p>
2 <a class="indexterm" name="id2618921"></a>
3 <a class="indexterm" name="id2618928"></a>
4 <a class="indexterm" name="id2618935"></a>
5 Well, you have reached one of the last chapters of this book. It is customary to attempt
6 to wrap up the theme and contents of a book in what is generally regarded as the
7 chapter that should draw conclusions. This book is a suspense thriller, and since
8 the plot of the stories told mostly lead you to bigger, better Samba-3 networking
9 solutions, it is perhaps appropriate to close this book with a few pertinent comments
10 regarding some of the things everyone can do to deliver a reliable Samba-3 network.
11 </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>
12 In a world so full of noise, how can the sparrow be heard?
13 </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="id2618959"></a>Introduction</h2></div></div></div><p>
14 <a class="indexterm" name="id2618967"></a>
15 The sparrow is a small bird whose sounds are drowned out by the noise of the busy
16 world it lives in. Likewise, the simple steps that can be taken to improve the
17 reliability and availability of a Samba network are often drowned out by the volume
18 of discussions about grandiose Samba clustering designs. This is not intended to
19 suggest that clustering is not important, because clearly it is. This chapter does not devote
20 itself to discussion of clustering because each clustering methodology uses its own
21 custom tools and methods. Only passing comments are offered concerning these methods.
22 </p><p>
23 <a class="indexterm" name="id2618997"></a>
24 <a class="indexterm" name="id2619004"></a>
25 <a class="indexterm" name="id2619011"></a>
26<a class="ulink" href="http://www.google.com/search?hl=en&amp;lr=&amp;ie=ISO-8859-1&amp;q=samba+cluster&amp;btnG=Google+Search" target="_top">A search</a>
27 for &#8220;<span class="quote">samba cluster</span>&#8221; produced 71,600 hits. And a search for &#8220;<span class="quote">highly available samba</span>&#8221;
28 and &#8220;<span class="quote">highly available windows</span>&#8221; produced an amazing number of references.
29 It is clear from the resources on the Internet that Windows file and print services
30 availability, reliability, and scalability are of vital interest to corporate network users.
31 </p><p>
32 <a class="indexterm" name="id2619044"></a>
33 So without further background, you can review a checklist of simple steps that
34 can be taken to ensure acceptable network performance while keeping costs of ownership
35 well under control.
36 </p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2619057"></a>Dissection and Discussion</h2></div></div></div><p>
37 <a class="indexterm" name="id2619065"></a>
38 <a class="indexterm" name="id2619071"></a>
39 If it is your purpose to get the best mileage out of your Samba servers, there is one rule that
40 must be obeyed. If you want the best, keep your implementation as simple as possible. You may
41 well be forced to introduce some complexities, but you should do so only as a last resort.
42 </p><p>
43 Simple solutions are likely to be easier to get right than are complex ones. They certainly
44 make life easier for your successor. Simple implementations can be more readily audited than can
45 complex ones.
46 </p><p>
47 <a class="indexterm" name="id2619093"></a>
48 <a class="indexterm" name="id2619100"></a>
49 Problems reported by users fall into three categories: configurations that do not work, those
50 that have broken behavior, and poor performance. The term <span class="emphasis"><em>broken behavior</em></span>
51 means that the function of a particular Samba component appears to work sometimes, but not at
52 others. The resulting intermittent operation is clearly unacceptable. An example of
53 <span class="emphasis"><em>broken behavior</em></span> known to many Windows networking users occurs when the
54 list of Windows machines in MS Explorer changes, sometimes listing machines that are running
55 and at other times not listing them even though the machines are in use on the network.
56 </p><p>
57 <a class="indexterm" name="id2619128"></a>
58 <a class="indexterm" name="id2619134"></a>
59 <a class="indexterm" name="id2619141"></a>
60 <a class="indexterm" name="id2619148"></a>
61 <a class="indexterm" name="id2619155"></a>
62 <a class="indexterm" name="id2619162"></a>
63 A significant number of reports concern problems with the <code class="literal">smbfs</code> file system
64 driver that is part of the Linux kernel, not part of Samba. Users continue to interpret that
65 <code class="literal">smbfs</code> is part of Samba, simply because Samba includes the front-end tools
66 that are used to manage <code class="literal">smbfs</code>-based file service connections. So, just
67 for the record, the tools <code class="literal">smbmnt</code>, <code class="literal">smbmount</code>,
68 <code class="literal">smbumount</code>, and <code class="literal">smbumnt</code> are front-end
69 facilities to core drivers that are supplied as part of the Linux kernel. These tools share a
70 common infrastructure with some Samba components, but they are not maintained as part of
71 Samba and are really foreign to it.
72 </p><p>
73 <a class="indexterm" name="id2619222"></a>
74 The new project, <code class="literal">cifsfs</code>, is destined to replace <code class="literal">smbfs</code>.
75 It, too, is not part of Samba, even though one of the Samba Team members is a prime mover in
76 this project.
77 </p><p>
78 Table 13.1 lists typical causes of:
79 </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>
80 <a class="indexterm" name="id2619516"></a>
81 It is obvious to all that the first requirement (as a matter of network hygiene) is to eliminate
82 problems that affect basic network operation. This book has provided sufficient working examples
83 to help you to avoid all these problems.
84 </p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2619530"></a>Guidelines for Reliable Samba Operation</h2></div></div></div><p>
85 <a class="indexterm" name="id2619538"></a>
86 <a class="indexterm" name="id2619545"></a>
87 Your objective is to provide a network that works correctly, can grow at all times, is resilient
88 at times of extreme demand, and can scale to meet future needs. The following subject areas provide
89 pointers that can help you today.
90 </p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2619557"></a>Name Resolution</h3></div></div></div><p>
91 There are three basic current problem areas: bad hostnames, routed networks, and network collisions.
92 These are covered in the following discussion.
93 </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2619568"></a>Bad Hostnames</h4></div></div></div><p>
94 <a class="indexterm" name="id2619576"></a>
95 <a class="indexterm" name="id2619586"></a>
96 <a class="indexterm" name="id2619592"></a>
97 <a class="indexterm" name="id2619599"></a>
98 <a class="indexterm" name="id2619606"></a>
99 When configured as a DHCP client, a number of Linux distributions set the system hostname
100 to <code class="constant">localhost</code>. If the parameter <em class="parameter"><code>netbios name</code></em> is not
101 specified to something other than <code class="constant">localhost</code>, the Samba server appears
102 in the Windows Explorer as <code class="constant">LOCALHOST</code>. Moreover, the entry in the <code class="filename">/etc/hosts</code>
103 on the Linux server points to IP address <code class="constant">127.0.0.1</code>. This means that
104 when the Windows client obtains the IP address of the Samba server called <code class="constant">LOCALHOST</code>,
105 it obtains the IP address <code class="constant">127.0.0.1</code> and then proceeds to attempt to
106 set up a NetBIOS over TCP/IP connection to it. This cannot work, because that IP address is
107 the local Windows machine itself. Hostnames must be valid for Windows networking to function
108 correctly.
109 </p><p>
110 <a class="indexterm" name="id2619661"></a>
111 A few sites have tried to name Windows clients and Samba servers with a name that begins
112 with the digits 1-9. This does not work either because it may result in the client or
113 server attempting to use that name as an IP address.
114 </p><p>
115 <a class="indexterm" name="id2619675"></a>
116 <a class="indexterm" name="id2619684"></a>
117 A Samba server called <code class="constant">FRED</code> in a NetBIOS domain called <code class="constant">COLLISION</code>
118 in a network environment that is part of the fully-qualified Internet domain namespace known
119 as <code class="constant">parrots.com</code>, results in DNS name lookups for <code class="constant">fred.parrots.com</code>
120 and <code class="constant">collision.parrots.com</code>. It is therefore a mistake to name the domain
121 (workgroup) <code class="constant">collision.parrots.com</code>, since this results in DNS lookup
122 attempts to resolve <code class="constant">fred.parrots.com.parrots.com</code>, which most likely
123 fails given that you probably do not have this in your DNS namespace.
124 </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
125 <a class="indexterm" name="id2619728"></a>
126 <a class="indexterm" name="id2619738"></a>
127 <a class="indexterm" name="id2619744"></a>
128 An Active Directory realm called <code class="constant">collision.parrots.com</code> is perfectly okay,
129 although it too must be capable of being resolved via DNS, something that functions correctly
130 if Windows 200x ADS has been properly installed and configured.
131 </p></div></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2619760"></a>Routed Networks</h4></div></div></div><p>
132 <a class="indexterm" name="id2619768"></a>
133 <a class="indexterm" name="id2619775"></a>
134 <a class="indexterm" name="id2619784"></a>
135 NetBIOS networks (Windows networking with NetBIOS over TCP/IP enabled) makes extensive use
136 of UDP-based broadcast traffic, as you saw during the exercises in <a class="link" href="primer.html" title="Chapter 16. Networking Primer">&#8220;Networking Primer&#8221;</a>.
137 </p><p>
138 <a class="indexterm" name="id2619804"></a>
139 <a class="indexterm" name="id2619811"></a>
140 <a class="indexterm" name="id2619818"></a>
141 UDP broadcast traffic is not forwarded by routers. This means that NetBIOS broadcast-based
142 networking cannot function across routed networks (i.e., multi-subnet networks) unless
143 special provisions are made:
144 </p><div class="itemizedlist"><ul type="disc"><li><p>
145 <a class="indexterm" name="id2619835"></a>
146 <a class="indexterm" name="id2619841"></a>
147 <a class="indexterm" name="id2619848"></a>
148 Either install on every Windows client an LMHOSTS file (located in the directory
149 <code class="filename">C:\windows\system32\drivers\etc</code>). It is also necessary to
150 add to the Samba server <code class="filename">smb.conf</code> file the parameters <em class="parameter"><code>remote announce</code></em>
151 and <em class="parameter"><code>remote browse sync</code></em>. For more information, refer to the online
152 manual page for the <code class="filename">smb.conf</code> file.
153 </p></li><li><p>
154 <a class="indexterm" name="id2619894"></a>
155 Or configure Samba as a WINS server, and configure all network clients to use that
156 WINS server in their TCP/IP configuration.
157 </p></li></ul></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
158 <a class="indexterm" name="id2619911"></a>
159 <a class="indexterm" name="id2619920"></a>
160 The use of DNS is not an acceptable substitute for WINS. DNS does not store specific
161 information regarding NetBIOS networking particulars that get stored in the WINS
162 name resolution database and that Windows clients require and depend on.
163 </p></div></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2619933"></a>Network Collisions</h4></div></div></div><p>
164 <a class="indexterm" name="id2619941"></a>
165 <a class="indexterm" name="id2619950"></a>
166 <a class="indexterm" name="id2619959"></a>
167 <a class="indexterm" name="id2619966"></a>
168 Excessive network activity causes NetBIOS network timeouts. Timeouts may result in
169 blue screen of death (BSOD) experiences. High collision rates may be caused by excessive
170 UDP broadcast activity, by defective networking hardware, or through excessive network
171 loads (another way of saying that the network is poorly designed).
172 </p><p>
173 The use of WINS is highly recommended to reduce network broadcast traffic, as outlined
174 in <a class="link" href="primer.html" title="Chapter 16. Networking Primer">&#8220;Networking Primer&#8221;</a>.
175 </p><p>
176 <a class="indexterm" name="id2619995"></a>
177 <a class="indexterm" name="id2620002"></a>
178 <a class="indexterm" name="id2620009"></a>
179 Under no circumstances should the facility be supported by many routers, known as <code class="constant">NetBIOS
180 forwarding</code>, unless you know exactly what you are doing. Inappropriate use of this
181 facility can result in UDP broadcast storms. In one case in 1999, a university network became
182 unusable due to NetBIOS forwarding being enabled on all routers. The problem was discovered during performance
183 testing of a Samba server. The maximum throughput on a 100-Base-T (100 MB/sec) network was
184 less than 15 KB/sec. After the NetBIOS forwarding was turned off, file transfer performance
185 immediately returned to 11 MB/sec.
186 </p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2620033"></a>Samba Configuration</h3></div></div></div><p>
187 As a general rule, the contents of the <code class="filename">smb.conf</code> file should be kept as simple as possible.
188 No parameter should be specified unless you know it is essential to operation.
189 </p><p>
190 <a class="indexterm" name="id2620052"></a>
191 <a class="indexterm" name="id2620060"></a>
192 <a class="indexterm" name="id2620066"></a>
193 Many UNIX administrators like to fully document the settings in the <code class="filename">smb.conf</code> file. This is a
194 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>
195 process every time the file timestamp changes (or, on systems where this does not work, every 20 seconds or so).
196 </p><p>
197 As the size of the <code class="filename">smb.conf</code> file grows, the risk of introducing parsing errors also increases.
198 It is recommended to keep a fully documented <code class="filename">smb.conf</code> file on hand, and then to operate Samba only
199 with an optimized file.
200 </p><p><a class="indexterm" name="id2620116"></a>
201 The preferred way to maintain a documented file is to call it something like <code class="filename">smb.conf.master</code>.
202 You can generate the optimized file by executing:
203</p><pre class="screen">
204<code class="prompt">root# </code> testparm -s smb.conf.master &gt; smb.conf
205</pre><p>
206 You should carefully observe all warnings issued. It is also a good practice to execute the following
207 command to confirm correct interpretation of the <code class="filename">smb.conf</code> file contents:
208</p><pre class="screen">
209<code class="prompt">root# </code> testparm
210Load smb config files from /etc/samba/smb.conf
211Can't find include file /etc/samba/machine.
212Processing section "[homes]"
213Processing section "[print$]"
214Processing section "[netlogon]"
215Processing section "[Profiles]"
216Processing section "[printers]"
217Processing section "[media]"
218Processing section "[data]"
219Processing section "[cdr]"
220Processing section "[apps]"
221Loaded services file OK.
222'winbind separator = +' might cause problems with group membership.
223Server role: ROLE_DOMAIN_PDC
224Press enter to see a dump of your service definitions
225</pre><p>
226 <a class="indexterm" name="id2620176"></a>
227 You now, of course, press the enter key to complete the command, or else abort it by pressing Ctrl-C.
228 The important thing to note is the noted Server role, as well as warning messages. Noted configuration
229 conflicts must be remedied before proceeding. For example, the following error message represents a
230 common fatal problem:
231</p><pre class="screen">
232ERROR: both 'wins support = true' and 'wins server = &lt;server list&gt;'
233cannot be set in the smb.conf file. nmbd will abort with this setting.
234</pre><p>
235 </p><p>
236 <a class="indexterm" name="id2620203"></a>
237 <a class="indexterm" name="id2620210"></a>
238 <a class="indexterm" name="id2620217"></a>
239 There are two parameters that can cause severe network performance degradation: <em class="parameter"><code>socket options</code></em>
240 and <em class="parameter"><code>socket address</code></em>. The <em class="parameter"><code>socket options</code></em> parameter was often necessary
241 when Samba was used with the Linux 2.2.x kernels. Later kernels are largely self-tuning and seldom benefit from
242 this parameter being set. Do not use either parameter unless it has been proven necessary to use them.
243 </p><p>
244 <a class="indexterm" name="id2620251"></a>
245 <a class="indexterm" name="id2620258"></a>
246 <a class="indexterm" name="id2620265"></a>
247 <a class="indexterm" name="id2620272"></a>
248 Another <code class="filename">smb.conf</code> parameter that may cause severe network performance degradation is the
249 <em class="parameter"><code>strict sync</code></em> parameter. Do not use this at all. There is no good reason
250 to use this with any modern Windows client. The <em class="parameter"><code>strict sync</code></em> is often
251 used with the <em class="parameter"><code>sync always</code></em> parameter. This, too, can severely
252 degrade network performance, so do not set it; if you must, do so with caution.
253 </p><p>
254 <a class="indexterm" name="id2620313"></a>
255 <a class="indexterm" name="id2620320"></a>
256 <a class="indexterm" name="id2620327"></a>
257 <a class="indexterm" name="id2620334"></a>
258 Finally, many network administrators deliberately disable opportunistic locking support. While this
259 does not degrade Samba performance, it significantly degrades Windows client performance because
260 this disables local file caching on Windows clients and forces every file read and written to
261 invoke a network read or write call. If for any reason you must disable oplocks (opportunistic locking)
262 support, do so only on the share on which it is required. That way, all other shares can provide
263 oplock support for operations that are tolerant of it. See <a class="link" href="appendix.html#ch12dblck" title="Shared Data Integrity">&#8220;Shared Data Integrity&#8221;</a> for more
264 information.
265 </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2620360"></a>Use and Location of BDCs</h3></div></div></div><p>
266 <a class="indexterm" name="id2620368"></a>
267 <a class="indexterm" name="id2620374"></a>
268 <a class="indexterm" name="id2620381"></a>
269 <a class="indexterm" name="id2620388"></a>
270 <a class="indexterm" name="id2620395"></a>
271 On a network segment where there is a PDC and a BDC, the BDC carries the bulk of the network logon
272 processing. If the BDC is a heavily loaded server, the PDC carries a greater proportion of
273 authentication and logon processing. When a sole BDC on a routed network segment gets heavily
274 loaded, it is possible that network logon requests and authentication requests may be directed
275 to a BDC on a distant network segment. This significantly hinders WAN operations
276 and is undesirable.
277 </p><p>
278 <a class="indexterm" name="id2620413"></a>
279 <a class="indexterm" name="id2620420"></a>
280 As a general guide, instead of adding domain member servers to a network, you would be better advised
281 to add BDCs until there are fewer than 30 Windows clients per BDC. Beyond that ratio, you should add
282 domain member servers. This practice ensures that there are always sufficient domain controllers
283 to handle logon requests and authentication traffic.
284 </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2620435"></a>Use One Consistent Version of MS Windows Client</h3></div></div></div><p>
285 Every network client has its own peculiarities. From a management perspective, it is easier to deal
286 with one version of MS Windows that is maintained to a consistent update level than it is to deal
287 with a mixture of clients.
288 </p><p>
289 On a number of occasions, particular Microsoft service pack updates of a Windows server or client
290 have necessitated special handling from the Samba server end. If you want to remain sane, keep you
291 client workstation configurations consistent.
292 </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2620457"></a>For Scalability, Use SAN-Based Storage on Samba Servers</h3></div></div></div><p>
293 <a class="indexterm" name="id2620466"></a>
294 <a class="indexterm" name="id2620473"></a>
295 Many SAN-based storage systems permit more than one server to share a common data store.
296 Use of a shared SAN data store means that you do not need to use time- and resource-hungry data
297 synchronization techniques.
298 </p><p>
299 <a class="indexterm" name="id2620487"></a>
300 <a class="indexterm" name="id2620494"></a>
301 The use of a collection of relatively low-cost front-end Samba servers that are coupled to
302 a shared backend SAN data store permits load distribution while containing costs below that
303 of installing and managing a complex clustering facility.
304 </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2620507"></a>Distribute Network Load with MSDFS</h3></div></div></div><p>
305 <a class="indexterm" name="id2620515"></a>
306 <a class="indexterm" name="id2620522"></a>
307 Microsoft DFS (distributed file system) technology has been implemented in Samba. MSDFS permits
308 data to be accessed from a single share and yet to actually be distributed across multiple actual
309 servers. Refer to <span class="emphasis"><em>TOSHARG2</em></span>, Chapter 19, for information regarding
310 implementation of an MSDFS installation.
311 </p><p>
312 <a class="indexterm" name="id2620540"></a>
313 <a class="indexterm" name="id2620550"></a>
314 The combination of multiple backend servers together with a front-end server and use of MSDFS
315 can achieve almost the same as you would obtain with a clustered Samba server.
316 </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2620562"></a>Replicate Data to Conserve Peak-Demand Wide-Area Bandwidth</h3></div></div></div><p>
317 <a class="indexterm" name="id2620570"></a>
318 <a class="indexterm" name="id2620577"></a>
319 <a class="indexterm" name="id2620584"></a>
320 Consider using <code class="literal">rsync</code> to replicate data across the WAN during times
321 of low utilization. Users can then access the replicated data store rather than needing to do so
322 across the WAN. This works best for read-only data, but with careful planning can be
323 implemented so that modified files get replicated back to the point of origin. Be careful with your
324 implementation if you choose to permit modification and return replication of the modified file;
325 otherwise, you may inadvertently overwrite important data.
326 </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2620607"></a>Hardware Problems</h3></div></div></div><p>
327 <a class="indexterm" name="id2620615"></a>
328 <a class="indexterm" name="id2620622"></a>
329 <a class="indexterm" name="id2620629"></a>
330 <a class="indexterm" name="id2620636"></a>
331 <a class="indexterm" name="id2620645"></a>
332 <a class="indexterm" name="id2620654"></a>
333 Networking hardware prices have fallen sharply over the past 5 years. A surprising number
334 of Samba networking problems over this time have been traced to defective network interface
335 cards (NICs) or defective HUBs, switches, and cables.
336 </p><p>
337 <a class="indexterm" name="id2620671"></a>
338 Not surprising is the fact that network administrators do not like to be shown to have made
339 a bad decision. Money saved in buying low-cost hardware may result in high costs incurred
340 in corrective action.
341 </p><p>
342 <a class="indexterm" name="id2620684"></a>
343 <a class="indexterm" name="id2620691"></a>
344 <a class="indexterm" name="id2620698"></a>
345 <a class="indexterm" name="id2620705"></a>
346 <a class="indexterm" name="id2620712"></a>
347 Defective NICs, HUBs, and switches may appear as intermittent network access problems, intermittent
348 or persistent data corruption, slow network throughput, low performance, or even as BSOD
349 problems with MS Windows clients. In one case, a company updated several workstations with newer, faster
350 Windows client machines that triggered problems during logon as well as data integrity problems on
351 an older PC that was unaffected so long as the new machines were kept shut down.
352 </p><p>
353 Defective hardware problems may take patience and persistence before the real cause can be discovered.
354 </p><p>
355 <a class="indexterm" name="id2620736"></a>
356 Networking hardware defects can significantly impact perceived Samba performance, but defective
357 RAID controllers as well as SCSI and IDE hard disk controllers have also been known to impair Samba server
358 operations. One business came to this realization only after replacing a Samba installation with MS
359 Windows Server 2000 running on the same hardware. The root of the problem completely eluded the network
360 administrator until the entire server was replaced. While you may well think that this would never
361 happen to you, experience shows that given the right (unfortunate) circumstances, this can happen to anyone.
362 </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2620755"></a>Large Directories</h3></div></div></div><p>
363 There exist applications that create or manage directories containing many thousands of files. Such
364 applications typically generate many small files (less than 100 KB). At the best of times, under UNIX,
365 listing of the files in a directory that contains many files is slow. By default, Windows NT, 200x,
366 and XP Pro cause network file system directory lookups on a Samba server to be performed for both
367 the case preserving file name as well as for the mangled (8.3) file name. This incurs a huge overhead
368 on the Samba server that may slow down the system dramatically.
369 </p><p>
370 In an extreme case, the performance impact was dramatic. File transfer from the Samba server to a Windows
371 XP Professional workstation over 1 Gigabit Ethernet for 250-500 KB files was measured at approximately
372 30 MB/sec. But when tranferring a directory containing 120,000 files, all from 50KB to 60KB in size, the
373 transfer rate to the same workstation was measured at approximately 1.5 KB/sec. The net transfer was
374 on the order of a factor of 20-fold slower.
375 </p><p>
376 The symptoms that will be observed on the Samba server when a large directory is accessed will be that
377 aggregate I/O (typically blocks read) will be relatively low, yet the wait I/O times will be incredibly
378 long while at the same time the read queue is large. Close observation will show that the hard drive
379 that the file system is on will be thrashing wildly.
380 </p><p>
381 Samba-3.0.12 and later, includes new code that radically improves Samba perfomance. The secret to this is
382 really in the <a class="link" href="smb.conf.5.html#CASESENSITIVE" target="_top">case sensitive = True</a> line. This tells smbd never to scan
383 for case-insensitive versions of names. So if an application asks for a file called <code class="filename">FOO</code>,
384 and it can not be found by a simple stat call, then smbd will return "file not found" immediately without
385 scanning the containing directory for a version of a different case.
386 </p><p>
387 Canonicalize all the files in the directory to have one case, upper or lower - either will do. Then set up
388 a new custom share for the application as follows:
389 </p><pre class="screen">
390 [bigshare]
391 path = /data/xrayfiles/neurosurgeons/
392 read only = no
393 case sensitive = True
394 default case = upper
395 preserve case = no
396 short preserve case = no
397 </pre><p>
398 </p><p>
399 All files and directories under the <em class="parameter"><code>path</code></em> directory must be in the same case
400 as specified in the <code class="filename">smb.conf</code> stanza. This means that smbd will not be able to find lower case
401 filenames with these settings. Note, this is done on a per-share basis.
402 </p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2620859"></a>Key Points Learned</h2></div></div></div><p>
403 This chapter has touched in broad sweeps on a number of simple steps that can be taken
404 to ensure that your Samba network is resilient, scalable, and reliable, and that it
405 performs well.
406 </p><p>
407 Always keep in mind that someone is responsible to maintain and manage your design.
408 In the long term, that may not be you. Spare a thought for your successor and give him or
409 her an even break.
410 </p><p>
411 <a class="indexterm" name="id2620880"></a>
412 Last, but not least, you should not only keep the network design simple, but also be sure it is
413 well documented. This book may serve as your pattern for documenting every
414 aspect of your design, its implementation, and particularly the objects and assumptions
415 that underlie it.
416 </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>
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