disks-virtual.html

FreeBSD操作系统的详细使用手册

<var class="OPTION">-r</var> should be removed. For more information, please refer to the
<a href="http://www.FreeBSD.org/cgi/man.cgi?query=bsdlabel&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">bsdlabel</span>(8)</span></a> manual
page.</p>
</blockquote>
</div>

<p>The utility <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=mdconfig&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">mdconfig</span>(8)</span></a> is very
useful, however it asks many command lines to create a file-backed file system.
FreeBSD&nbsp;5.0 also comes with a tool called <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=mdmfs&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">mdmfs</span>(8)</span></a>, this program
configures a <a href="http://www.FreeBSD.org/cgi/man.cgi?query=md&sektion=4"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">md</span>(4)</span></a> disk using <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=mdconfig&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">mdconfig</span>(8)</span></a>, puts a
UFS file system on it using <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=newfs&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">newfs</span>(8)</span></a>, and mounts
it using <a href="http://www.FreeBSD.org/cgi/man.cgi?query=mount&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">mount</span>(8)</span></a>. For example,
if you want to create and mount the same file system image as above, simply type the
following:</p>

<div class="EXAMPLE"><a id="AEN25304" name="AEN25304"></a>
<p><b>Example 16-8. Configure and Mount a File-Backed Disk with <tt
class="COMMAND">mdmfs</tt></b></p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">dd if=/dev/zero of=<var
class="REPLACEABLE">newimage</var> bs=1k count=<var class="REPLACEABLE">5</var>k</kbd>
5120+0 records in
5120+0 records out
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">mdmfs -F <var
class="REPLACEABLE">newimage</var> -s <var class="REPLACEABLE">5</var>m md<var
class="REPLACEABLE">0</var> <var class="REPLACEABLE">/mnt</var></kbd>
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">df <var
class="REPLACEABLE">/mnt</var></kbd>
Filesystem 1K-blocks Used Avail Capacity  Mounted on
/dev/md0        4846    2  4458     0%    /mnt
</pre>
</div>

<p>If you use the option <var class="OPTION">md</var> without unit number, <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=mdmfs&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">mdmfs</span>(8)</span></a> will use <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=md&sektion=4"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">md</span>(4)</span></a> auto-unit
feature to automatically select an unused device. For more details about <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=mdmfs&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">mdmfs</span>(8)</span></a>, please refer
to the manual page.</p>
</div>

<div class="SECT2">
<h2 class="SECT2"><a id="DISKS-MD-FREEBSD4" name="DISKS-MD-FREEBSD4">16.12.3 Memory-Based
File System under FreeBSD&nbsp;4.X</a></h2>

<p>The <a href="http://www.FreeBSD.org/cgi/man.cgi?query=md&sektion=4"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">md</span>(4)</span></a> driver is a
simple, efficient means to create memory file systems under FreeBSD&nbsp;4.X. <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=malloc&sektion=9"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">malloc</span>(9)</span></a> is used to
allocate the memory.</p>

<p>Simply take a file system you have prepared with, for example, <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=vnconfig&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">vnconfig</span>(8)</span></a>, and:</p>

<div class="EXAMPLE"><a id="AEN25348" name="AEN25348"></a>
<p><b>Example 16-9. md Memory Disk under FreeBSD&nbsp;4.X</b></p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">dd if=<var
class="REPLACEABLE">newimage</var> of=/dev/md<var class="REPLACEABLE">0</var></kbd>
5120+0 records in
5120+0 records out
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">mount /dev/md<var
class="REPLACEABLE">0c</var> <var class="REPLACEABLE">/mnt</var></kbd>
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">df <var
class="REPLACEABLE">/mnt</var></kbd>
Filesystem  1K-blocks     Used    Avail Capacity  Mounted on
/dev/md0c        4927        1     4532     0%    /mnt
</pre>
</div>

<p>For more details, please refer to <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=md&sektion=4"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">md</span>(4)</span></a> manual page.</p>
</div>

<div class="SECT2">
<h2 class="SECT2"><a id="DISKS-MD-FREEBSD5" name="DISKS-MD-FREEBSD5">16.12.4 Memory-Based
File System under FreeBSD&nbsp;5.X</a></h2>

<p>The same tools are used for memory-based and file-backed file systems: <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=mdconfig&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">mdconfig</span>(8)</span></a> or <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=mdmfs&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">mdmfs</span>(8)</span></a>. The storage
for memory-based file system is allocated with <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=malloc&sektion=9"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">malloc</span>(9)</span></a>.</p>

<div class="EXAMPLE"><a id="AEN25381" name="AEN25381"></a>
<p><b>Example 16-10. Creating a New Memory-Based Disk with <tt
class="COMMAND">mdconfig</tt></b></p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">mdconfig -a -t malloc -s <var
class="REPLACEABLE">5</var>m -u <var class="REPLACEABLE">1</var></kbd>
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">newfs -U md<var
class="REPLACEABLE">1</var></kbd>
/dev/md1: 5.0MB (10240 sectors) block size 16384, fragment size 2048
    using 4 cylinder groups of 1.27MB, 81 blks, 256 inodes.
    with soft updates
super-block backups (for fsck -b #) at:
 32, 2624, 5216, 7808
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">mount /dev/md<var
class="REPLACEABLE">1</var> <var class="REPLACEABLE">/mnt</var></kbd>
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">df <var
class="REPLACEABLE">/mnt</var></kbd>
Filesystem 1K-blocks Used Avail Capacity  Mounted on
/dev/md1        4846    2  4458     0%    /mnt
</pre>
</div>

<div class="EXAMPLE"><a id="AEN25399" name="AEN25399"></a>
<p><b>Example 16-11. Creating a New Memory-Based Disk with <tt
class="COMMAND">mdmfs</tt></b></p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">mdmfs -M -s <var
class="REPLACEABLE">5</var>m md<var class="REPLACEABLE">2</var> <var
class="REPLACEABLE">/mnt</var></kbd>
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">df <var
class="REPLACEABLE">/mnt</var></kbd>
Filesystem 1K-blocks Used Avail Capacity  Mounted on
/dev/md2        4846    2  4458     0%    /mnt
</pre>
</div>

<p>Instead of using a <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=malloc&sektion=9"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">malloc</span>(9)</span></a> backed file
system, it is possible to use swap, for that just replace <var
class="OPTION">malloc</var> with <var class="OPTION">swap</var> in the command line of <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=mdconfig&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">mdconfig</span>(8)</span></a>. The <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=mdmfs&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">mdmfs</span>(8)</span></a> utility by
default (without <var class="OPTION">-M</var>) creates a swap-based disk. For more
details, please refer to <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=mdconfig&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">mdconfig</span>(8)</span></a> and <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=mdmfs&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">mdmfs</span>(8)</span></a> manual
pages.</p>
</div>

<div class="SECT2">
<h2 class="SECT2"><a id="AEN25430" name="AEN25430">16.12.5 Detaching a Memory Disk from
the System</a></h2>

<p>When a memory-based or file-based file system is not used, you should release all
resources to the system. The first thing to do is to unmount the file system, then use <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=mdconfig&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">mdconfig</span>(8)</span></a> to detach
the disk from the system and release the resources.</p>

<p>For example to detach and free all resources used by <tt
class="FILENAME">/dev/md4</tt>:</p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">mdconfig -d -u <var
class="REPLACEABLE">4</var></kbd>
</pre>

<p>It is possible to list information about configured <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=md&sektion=4"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">md</span>(4)</span></a> devices in using
the command <tt class="COMMAND">mdconfig -l</tt>.</p>

<p>For FreeBSD&nbsp;4.X, <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=vnconfig&sektion=8"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">vnconfig</span>(8)</span></a> is used to
detach the device. For example to detach and free all resources used by <tt
class="FILENAME">/dev/vn4</tt>:</p>

<pre class="SCREEN">
<samp class="PROMPT">#</samp> <kbd class="USERINPUT">vnconfig -u vn<var
class="REPLACEABLE">4</var></kbd>
</pre>
</div>
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