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<h1 class="topictitle1">Concepts for virtual storage</h1>
<div><p>This topic provides general information about virtual storage,
including descriptions and instructions for use.</p>
<p>When you use virtual storage, you create virtual tape, CD, or DVD images
that exist on your server disk units. The objects that virtual storage uses
are as follows:</p>
<div class="section"><h4 class="sectiontitle">Virtual storage device</h4><p>A <span class="uicontrol">virtual storage
device</span> is a device description that supports virtual storage,
like an actual tape or optical device description supports actual storage.
One to 35 virtual storage tape device descriptions and one to 35 virtual storage
optical device descriptions can be active at a time on the server.</p>
<p>You
create a virtual tape device by selecting the RSRCNAME(*VRT) or TYPE(63B0)
parameters on the Create Device Description (Tape) or (CRTDEVTAP) command.</p>
<p>You
create a virtual optical device by selecting the RSRCNAME(*VRT) or TYPE(632B)
parameters in Create Device Description (Optical) or (CRTDEVOPT) command.</p>
</div>
<div class="section"><h4 class="sectiontitle">Image catalog</h4><p>An <span class="uicontrol">image catalog</span> is
an object that can contain up to 256 image catalog entries. Each catalog is
associated with one user-specified integrated file system directory. The system-recognized
identifier for the object type is *IMGCLG. Image catalogs can have the following
statuses:</p>
<dl><dt class="dlterm">Ready</dt>
<dd> All of the loaded and mounted image catalog entries are available for
use by the virtual storage device. The image catalog can be made
ready by using the LODIMGCLG (Load Image Catalog) command with the parameter
OPTION(*LOAD).</dd>
<dt class="dlterm">Not Ready</dt>
<dd>None of the image catalog entries in the image catalog are available for
use by the virtual storage device.</dd>
</dl>
<p>You can view or change image catalogs by using the Work
with Image Catalogs (WRKIMGCLG) command.</p>
</div>
<div class="section"><h4 class="sectiontitle">Write protection</h4><p><span class="uicontrol">Write protection</span> refers
to whether you have enabled the write protection switch for an image catalog
entry. The status for write protection are as follows:</p>
<dl><dt class="dlterm">Y</dt>
<dd>Write protection is set for the image catalog entry. You cannot write
to the virtual image associated with the image catalog entry.</dd>
<dt class="dlterm">N</dt>
<dd>Write protection is not set for the image catalog entry. You can write
to the virtual image associated with the image catalog entry.</dd>
</dl>
<div class="p"><span class="uicontrol">For optical use only</span> <div class="note"><span class="notetitle">Note:</span> If the
access for an optical image catalog entry is *READWRITE, you set the write
protection switch to Y or N. If the access for the optical image catalog
entry is *READONLY, the write protection switch is always set to Y.</div>
</div>
<p>You
can view or change image catalog entries by using the Work with Image Catalog
Entries (WRKIMGCLGE) command. The WRKIMGCLGE command indicates if the image
catalog is in a Ready state or a Not ready state, and you can use this command
to change image catalog entries whether the image catalog is in a Ready state
or a Not ready state.</p>
<p>You can change image catalog entries by using
the Load/Unload/Mount IMGCLG Entry (LODIMGCLGE) command or by typing <samp class="codeph">GO
IMGCLG</samp> at a command line.</p>
</div>
<div class="section"><h4 class="sectiontitle">Virtual image</h4><p>A <span class="uicontrol">virtual image</span> is
an object that contains the data that is typically on physical media. The
virtual image is a stream file that resides in the integrated file system.
In a backup and recovery scenario, you can also span virtual images.</p>
</div>
</div>
<div>
<ul class="ullinks">
<li class="ulchildlink"><img src="./delta.gif" alt="Start of change" /><strong><a href="rzam4virtualwhatis.htm">Benefits of virtual storage</a></strong><img src="./deltaend.gif" alt="End of change" /><br />
Virtual storage can help eliminate media errors and user intervention and can increase system availability.</li>
<li class="ulchildlink"><img src="./delta.gif" alt="Start of change" /><strong><a href="rzam4catalogshodowing.htm">Catalog Shadowing</a></strong><img src="./deltaend.gif" alt="End of change" /><br />
Use catalog shadowing to create a copy of an existing image catalog.</li>
</ul>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <img src="./delta.gif" alt="Start of change" /><a href="rzam4virtualstorage.htm" title="Virtual storage consists of objects that, when used together, imitate tape, CD, DVD, and write-once read-many (WORM) media on your disk units. The imitated media appear to the server to be actual media.">Virtual storage</a><img src="./deltaend.gif" alt="End of change" /></div>
</div>
<div class="relref"><strong>Related reference</strong><br />
<div><a href="../cl/wrkimgclg.htm">Work with Image Catalogs (WRKIMGCLG)</a></div>
<div><a href="../cl/wrkimgclge.htm">Work with Image Catalog Entries (WRKIMGCLGE)</a></div>
<div><a href="../cl/lodimgclge.htm">Load/Unload/Mount IMGCLG Entry (LODIMGCLGE)</a></div>
</div>
<div class="relinfo"><strong>Related information</strong><br />
<div><a href="../books/sc415302.pdf" target="_blank">iSeries Security Reference</a></div>
</div>
</div>
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