svn commit: r44647 - head/en_US.ISO8859-1/books/handbook/disks
Dru Lavigne
dru at FreeBSD.org
Thu Apr 24 18:24:49 UTC 2014
Author: dru
Date: Thu Apr 24 18:24:48 2014
New Revision: 44647
URL: http://svnweb.freebsd.org/changeset/doc/44647
Log:
Editorial review of Attaching and Detaching Existing Images.
More commits to come to finish review of this chapter.
Sponsored by: iXsystems
Modified:
head/en_US.ISO8859-1/books/handbook/disks/chapter.xml
Modified: head/en_US.ISO8859-1/books/handbook/disks/chapter.xml
==============================================================================
--- head/en_US.ISO8859-1/books/handbook/disks/chapter.xml Thu Apr 24 18:20:14 2014 (r44646)
+++ head/en_US.ISO8859-1/books/handbook/disks/chapter.xml Thu Apr 24 18:24:48 2014 (r44647)
@@ -1989,44 +1989,67 @@ scsibus1:
</info>
<para>In addition to physical disks, &os; also supports
- the creation and use of memory disks.</para>
+ the creation and use of memory disks. One possible use for a
+ memory disk is to access the contents of an
+ <acronym>ISO</acronym> file system without the overhead of first
+ burning it to a <acronym>CD</acronym> or <acronym>DVD</acronym>,
+ then mounting the <acronym>CD/DVD</acronym> media.</para>
+
+ <para>In &os;, the &man.md.4; driver is used to provide support
+ for memory disks. The <filename>GENERIC</filename> kernel
+ includes this driver. When using a custom kernel
+ configuration file, ensure it includes this line:</para>
- <indexterm>
- <primary>disks</primary>
- <secondary>memory</secondary>
- </indexterm>
+ <programlisting>device md</programlisting>
<sect2 xml:id="disks-mdconfig">
<title>Attaching and Detaching Existing Images</title>
<indexterm>
<primary>disks</primary>
- <secondary>file-backed</secondary>
+ <secondary>memory</secondary>
</indexterm>
- <para>&man.mdconfig.8; is used to configure and enable memory
- disks, &man.md.4;, under &os;. To use &man.mdconfig.8;,
- &man.md.4; must be first loaded. When using a custom kernel
- configuration file, ensure it includes this line:</para>
+ <para>To mount an existing file system image, use
+ <command>mdconfig</command> to specify the name of the
+ <acronym>ISO</acronym> file and a free unit number. Then,
+ refer to that unit number to mount it on an existing mount
+ point. Once mounted, the files in the <acronym>ISO</acronym>
+ will appear in the mount point. This example attaches
+ <replaceable>diskimage.iso</replaceable> to the memory device
+ <filename>/dev/md0</filename> then mounts that memory device
+ on <filename>/mnt</filename>:</para>
- <programlisting>device md</programlisting>
+ <screen>&prompt.root; <userinput>mdconfig -f <replaceable>diskimage.iso</replaceable> -u <replaceable>0</replaceable></userinput>
+&prompt.root; <userinput>mount /dev/md<replaceable>0</replaceable> <replaceable>/mnt</replaceable></userinput></screen>
- <para>&man.mdconfig.8; supports several types of memory backed
- virtual disks: memory disks allocated with &man.malloc.9; and
- memory disks using a file or swap space as backing. One
- possible use is the mounting of <acronym>CD</acronym>
- images.</para>
+ <para>If a unit number is not specified with
+ <option>-u</option>, <command>mdconfig</command> will
+ automatically allocate an unused memory device and output
+ the name of the allocated unit, such
+ as <filename>md4</filename>. Refer to &man.mdconfig.8;
+ for more details about this command and its options.</para>
+
+ <para>When a memory disk is no
+ longer in use, its resources should be released back to
+ the system. First, unmount the file system, then use
+ <command>mdconfig</command> to detach the disk from the system and
+ release its resources. To continue this example:</para>
- <para>To mount an existing file system image:</para>
+ <screen>&prompt.root; <userinput>umount /mnt</userinput>
+&prompt.root; <userinput>mdconfig -d -u <replaceable>0</replaceable></userinput></screen>
- <example>
- <title>Using <command>mdconfig</command> to Mount an Existing
- File System Image</title>
+ <para>To determine if any memory disks are still attached to the
+ system, type <command>mdconfig -l</command>.</para>
+ </sect2>
- <screen>&prompt.root; <userinput>mdconfig -f <replaceable>diskimage.iso</replaceable> -u <replaceable>0</replaceable></userinput>
-&prompt.root; <userinput>mount /dev/md<replaceable>0</replaceable> <replaceable>/mnt</replaceable></userinput></screen>
- </example>
+ <sect2 xml:id="disks-md-freebsd5">
+ <title>Creating a Memory Disk</title>
+ <indexterm>
+ <primary>disks</primary>
+ <secondary>memory file system</secondary>
+ </indexterm>
<para>To create a new file system image with
&man.mdconfig.8;:</para>
@@ -2050,12 +2073,32 @@ Filesystem 1K-blocks Used Avail Capacity
/dev/md0a 4710 4 4330 0% /mnt</screen>
</example>
- <para>If unit number is not specified with
- <option>-u</option>, &man.mdconfig.8; uses the
- &man.md.4; automatic allocation to select an unused device.
- The name of the allocated unit will be output to stdout, such
- as <filename>md4</filename>. Refer to &man.mdconfig.8;
- for more details about.</para>
+ <para>For a memory-based file system, <quote>swap
+ backing</quote> should normally be used. This does not mean
+ that the memory disk will be swapped out to disk by default,
+ but rather that the memory disk will be allocated from a
+ memory pool which can be swapped out to disk if needed. It is
+ also possible to create memory-based disks which are
+ &man.malloc.9; backed, but using large malloc backed memory
+ disks can result in a system panic if the kernel runs out of
+ memory.</para>
+
+ <example>
+ <title>Creating a New Memory-Based Disk with
+ <command>mdconfig</command></title>
+
+ <screen>&prompt.root; <userinput>mdconfig -a -t swap -s <replaceable>5</replaceable>m -u <replaceable>1</replaceable></userinput>
+&prompt.root; <userinput>newfs -U md<replaceable>1</replaceable></userinput>
+/dev/md1: 5.0MB (10240 sectors) block size 16384, fragment size 2048
+ using 4 cylinder groups of 1.27MB, 81 blks, 192 inodes.
+ with soft updates
+super-block backups (for fsck -b #) at:
+ 160, 2752, 5344, 7936
+&prompt.root; <userinput>mount /dev/md<replaceable>1</replaceable> <replaceable>/mnt</replaceable></userinput>
+&prompt.root; <userinput>df <replaceable>/mnt</replaceable></userinput>
+Filesystem 1K-blocks Used Avail Capacity Mounted on
+/dev/md1 4718 4 4338 0% /mnt</screen>
+ </example>
<para>While &man.mdconfig.8; is useful, it takes several
command lines to create a file-backed file system. &os; also
@@ -2087,58 +2130,6 @@ Filesystem 1K-blocks Used Avail Capacity
<primary>disks</primary>
<secondary>detaching a memory disk</secondary>
</indexterm>
-
- <para>When a memory-based or file-based file system is no
- longer in use, its resources should be released back to
- the system. First, unmount the file system, then use
- &man.mdconfig.8; to detach the disk from the system and
- release the resources.</para>
-
- <para>For example, to detach and free all resources used by
- <filename>/dev/md4</filename>:</para>
-
- <screen>&prompt.root; <userinput>mdconfig -d -u <replaceable>4</replaceable></userinput></screen>
-
- <para>It is possible to list information about configured
- &man.md.4; devices by running
- <command>mdconfig -l</command>.</para>
- </sect2>
-
- <sect2 xml:id="disks-md-freebsd5">
- <title>Creating a Memory Disk</title>
-
- <indexterm>
- <primary>disks</primary>
- <secondary>memory file system</secondary>
- </indexterm>
-
- <para>For a memory-based file system, <quote>swap
- backing</quote> should normally be used. This does not mean
- that the memory disk will be swapped out to disk by default,
- but rather that the memory disk will be allocated from a
- memory pool which can be swapped out to disk if needed. It is
- also possible to create memory-based disks which are
- &man.malloc.9; backed, but using large malloc backed memory
- disks can result in a system panic if the kernel runs out of
- memory.</para>
-
- <example>
- <title>Creating a New Memory-Based Disk with
- <command>mdconfig</command></title>
-
- <screen>&prompt.root; <userinput>mdconfig -a -t swap -s <replaceable>5</replaceable>m -u <replaceable>1</replaceable></userinput>
-&prompt.root; <userinput>newfs -U md<replaceable>1</replaceable></userinput>
-/dev/md1: 5.0MB (10240 sectors) block size 16384, fragment size 2048
- using 4 cylinder groups of 1.27MB, 81 blks, 192 inodes.
- with soft updates
-super-block backups (for fsck -b #) at:
- 160, 2752, 5344, 7936
-&prompt.root; <userinput>mount /dev/md<replaceable>1</replaceable> <replaceable>/mnt</replaceable></userinput>
-&prompt.root; <userinput>df <replaceable>/mnt</replaceable></userinput>
-Filesystem 1K-blocks Used Avail Capacity Mounted on
-/dev/md1 4718 4 4338 0% /mnt</screen>
- </example>
-
<example>
<title>Creating a New Memory-Based Disk with
<command>mdmfs</command></title>
More information about the svn-doc-all
mailing list