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1 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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2 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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3 <html xmlns="http://www.w3.org/1999/xhtml">
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4 <head>
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5 <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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6 <title>digilib -- Digital Image Library</title>
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7 </head>
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8 <body>
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9 <table border="0" cellspacing="0" cellpadding="10">
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10 <tr>
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11 <td bgcolor="#a0a0a0"> </td>
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12 <td>
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13 <img src="images/digilib-logo-big.png" align="left" />
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14 <h1>
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15 <tt>digilib</tt>
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16 -- a versatile image viewing environment for the internet
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17 </h1>
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18 </td>
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19 </tr>
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20 <tr>
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21 <td bgcolor="#a0a0a0" valign="top" align="right">
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22 <p>
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23 <b><a href="index.html">Info</a>
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24 </b>
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25 </p>
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26 <p>
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27 <b><a href="http://developer.berlios.de/projects/digilib/">Project</a>
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28 </b>
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29 </p>
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30 <p>
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31 <b><a href="http://developer.berlios.de/project/showfiles.php?group_id=251">Download</a>
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32 </b>
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33 </p>
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34 <p>
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35 <b><a href="http://developer.berlios.de/docman/?group_id=251">Docs</a>
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36 </b>
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37 </p>
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38 <p>
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39 <b><a href="tips.html">Tips</a>
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40 </b>
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41 </p>
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42 <p>
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43 <b><a href="http://hg.berlios.de/repos/digilib">Source</a>
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44 </b>
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45 </p>
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46 </td>
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47 <td>
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48
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49
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50 <p>Some tips for running digilib</p>
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51 <ul>
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52 <li>
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53 <a href="#vm_settings">Java VM settings for digilib</a>
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54 </li>
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55 <li>
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56 <a href="#prescaled_images">Prescaled images</a>
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57 </li>
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58 <li>
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59 <a href="installing_jai">Installing JAI</a>
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60 </li>
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61 </ul>
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62
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63 <h1 id="vm_settings">Java VM settings for digilib</h1>
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64
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65 <p>The Java virtual machine (Java-VM) only uses a fixed amount of memory for
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66 its operations. When an operation needs more memory than available it aborts
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67 with an error ("out of memory error").</p>
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68 <p>digilib can need a lot of memory depending on the size and type of images.
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69 Since digilib runs as a servlet under Tomcat its in the same VM as the Tomcat
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70 server.</p>
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71 <p>The amount of memory Tomcat (version 5.0) uses is configured by creating a
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72 "setenv.sh" script with a line</p>
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73 <pre> CATALINA_OPTS="-Xmx512m"
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74 </pre>
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75 <p>in Tomcat's "bin" directory (giving 512MB in this case).</p>
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76 <p>
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77 You can check the amount of memory your digilib instance has available on the
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78 bottom of the web page /server/dlConfig.jsp in your digilib instance (e.g. <a
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79 href="http://digilib.mpiwg-berlin.mpg.de/digitallibrary/server/dlConfig.jsp"
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80 class="external free" rel="nofollow">http://digilib.mpiwg-berlin.mpg.de/digitallibrary/server/dlConfig.jsp</a>).
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81 </p>
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82
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83 <h1 id="prescaled_images">Prescaled images</h1>
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84
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85 <p>You can provide any number of scaled-down versions of your images that
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86 digilib uses when a smaller version of an image is requested. Since less data
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87 has to be read and processed this can speed up digilib's performance quite a
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88 lot.</p>
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89 <p>The actual process is that the client requests a certain target size,
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90 digilib scans all available scaled-down versions of the same image, selects the
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91 smallest image that is larger than the requested size and scales it down to the
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92 requested size.</p>
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93 <p>The scaled-down versions of the image have to have the same file name as
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94 the original hi-res file. They can have a different type and extension (e.g.
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95 img002.jpg for img002.TIFF)</p>
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96 <p>The scaled down images have to be in the same subdirectory (the part that
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97 shows up in digilib's "fn" parameter) as the hi-res file. The first part of each
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98 directory tree is configured by the basedir-list parameter in
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99 digilib-config.xml.</p>
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100 <p>The sequence of directories in basedir-list is from hi-res to lo-res.
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101 Images must be present in the hires directory but they need not be present in
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102 all lower-res directories.</p>
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103 <p>e.g. if digilib-config.xml contains</p>
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104 <pre> <parameter name="basedir-list" value="/images:/scaled:/thumb" />
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105 </pre>
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106 <p>and a user requests the image "books/book1/page0002" digilib looks for</p>
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107 <pre> /thumb/books/book1/page0002.*
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108 /scaled/books/book1/page002.*
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109 /images/books/book1/page002.*
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110 </pre>
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111 <p>and uses the first image that is bigger than or equal to the requested
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112 size.</p>
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113 <p>
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114 For batch-prescaling our images we use a script called "scale-o-mat" that uses a
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115 lot of freely available imaging libraries (ImageMagick, libtiff, netpbm) and is
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116 available in our public CVS <a
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117 href="http://itgroup.mpiwg-berlin.mpg.de/cgi-bin/cvsweb.cgi/scaleomat/"
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118 class="external autonumber" rel="nofollow">[1]</a>. The script is given a
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119 hi-res base directory, a destination base directory, a destination size and a
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120 starting directory. It then processes all files in the starting directory and
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121 all its subdirectories and creates scaled images in corresponding directories
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122 under the destination base directory.
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123 </p>
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124 <p>We currently use prescaled thumbnails of 100 pixels and images for browser
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125 display of 1500 pixels. Remember that the prescaled image has to be larger (or
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126 the same size) than the requested image size!</p>
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127 <p>There is another optimization in digilib: if the requested image is exactly
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128 the same size and type as the prescaled image then the prescaled image is sent
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129 unmodified to the client which is a lot faster. So it makes sense to produce
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130 thumbnails of exactly 90 pixels width when they are used in an HTML page where
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131 all images are 90 pixels wide.</p>
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132
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133
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134 <h1 id="installing_jai">Installing JAI</h1>
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135
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136 <p>
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137 In principle you can install the <a
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138 href="http://java.sun.com/javase/technologies/desktop/media/jai/"
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139 class="external text" rel="nofollow">Java Advanced Imaging</a> JAR files (and
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140 native library files if available) in the /WEB-INF/lib/ directory of the digilib
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141 web application.
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142
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143 </p>
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144 <p>I found that in some cases digilib stopped reading TIFF files after a
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145 period of running. In these cases it helped to install the JAI files directly in
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146 the local Java installation (i.e. in the Java's /jre/lib/ext/ directory on
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147 linux).</p>
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148
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149
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150 <h1 id="mpiwg_setup">Sample setup</h1>
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151
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152 <p>The current digilib setup at the MPIWG (as of November 2005):</p>
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153 <ul>
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154 <li>
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155 One frontend server running the lightweight web-multiplexer <a
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156 href="http://www.apsis.ch/pound/" class="external text" rel="nofollow">pound</a>
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157 on port 80 that distributes requests to two servers runnning digilib
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158 </li>
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159 <li>
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160 the two servers run digilib under <a
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161 href="http://tomcat.apache.org/index.html" class="external text"
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162 rel="nofollow">Tomcat</a> on port 8080 without Apache
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163 <ul>
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164 <li>one server is the same machine as the frontend server (Linux, Dual
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165 2.4GHz Xeon, 2GB RAM)</li>
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166 <li>the other server is a separate, newer machine (Linux, Dual 1.8GHz
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167 Opteron, 2GB RAM)</li>
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168 </ul>
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169 </li>
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170 <li>
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171 the digilib instances (digilib 1.5.9c as of 22.11.2005) run on Tomcat on Java
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172 1.5.0_05 (or 1.4.2_06) with 1GB of <a href="#vm_settings">Java VM memory
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173 for digilib</a> (-Xmx1024m) with JAI (1.1.2_01) and JAI-ImageIO (1.0_01) <a
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174 href="#installing_jai">installed in the JRE</a>(!)
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175 </li>
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176 <li>both digilib servers access all image files over NFS (over GBit
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177 Ethernet) from a central file server (Solaris 8, Sun Fire 480, multiple RAIDs
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178 on Fibrechannel)</li>
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179 </ul>
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180
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181 </td>
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182 </tr>
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183 <tr>
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184 <td style="padding: 0px" align="left">
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185 <a href="http://developer.berlios.de"> <img
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186 src="http://developer.berlios.de/bslogo.php?group_id=0&type=1" width="124"
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187 height="32" border="0" alt="BerliOS Logo" /> </a>
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188 </td>
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189 <td></td>
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190 </tr>
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191 </table>
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192
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193 </body>
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194 </html> |
