svn commit: r44648 - head/en_US.ISO8859-1/books/handbook/disks
Dru Lavigne
dru at FreeBSD.org
Thu Apr 24 19:51:56 UTC 2014
Author: dru
Date: Thu Apr 24 19:51:56 2014
New Revision: 44648
URL: http://svnweb.freebsd.org/changeset/doc/44648
Log:
Finish editorial review of Memory Disks 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 18:24:48 2014 (r44647)
+++ head/en_US.ISO8859-1/books/handbook/disks/chapter.xml Thu Apr 24 19:51:56 2014 (r44648)
@@ -2030,6 +2030,11 @@ scsibus1:
as <filename>md4</filename>. Refer to &man.mdconfig.8;
for more details about this command and its options.</para>
+ <indexterm>
+ <primary>disks</primary>
+ <secondary>detaching a memory disk</secondary>
+ </indexterm>
+
<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
@@ -2044,48 +2049,26 @@ scsibus1:
</sect2>
<sect2 xml:id="disks-md-freebsd5">
- <title>Creating a Memory Disk</title>
+ <title>Creating a File- or Memory-Backed 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>
-
- <example>
- <title>Creating a New File-Backed Disk with
- <command>mdconfig</command></title>
-
- <screen>&prompt.root; <userinput>dd if=/dev/zero of=<replaceable>newimage</replaceable> bs=1k count=<replaceable>5</replaceable>k</userinput>
-5120+0 records in
-5120+0 records out
-&prompt.root; <userinput>mdconfig -a -t vnode -f <replaceable>newimage</replaceable> -u <replaceable>0</replaceable></userinput>
-&prompt.root; <userinput>bsdlabel -w md<replaceable>0</replaceable> auto</userinput>
-&prompt.root; <userinput>newfs md<replaceable>0</replaceable>a</userinput>
-/dev/md0a: 5.0MB (10224 sectors) block size 16384, fragment size 2048
- using 4 cylinder groups of 1.25MB, 80 blks, 192 inodes.
-super-block backups (for fsck -b #) at:
- 160, 2720, 5280, 7840
-&prompt.root; <userinput>mount /dev/md<replaceable>0</replaceable>a <replaceable>/mnt</replaceable></userinput>
-&prompt.root; <userinput>df <replaceable>/mnt</replaceable></userinput>
-Filesystem 1K-blocks Used Avail Capacity Mounted on
-/dev/md0a 4710 4 4330 0% /mnt</screen>
- </example>
-
- <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>
+ <para>&os; also supports memory disks where the storage to use
+ is allocated from either a hard disk or an area of memory.
+ The first method is commonly referred to as a file-backed file
+ system and the second method as a memory-backed file system.
+ Both types can be created using
+ <command>mdconfig</command>.</para>
+
+ <para>To create a new memory-backed file system, specify a type
+ of <literal>swap</literal> and the size of the memory disk to
+ create. Then, format the memory disk with a file system and
+ mount as usual. This example creates a 5M memory disk on unit
+ <literal>1</literal>. That memory disk is then formatted with
+ the <acronym>UFS</acronym> file system before it is
+ mounted:</para>
<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>
@@ -2098,47 +2081,55 @@ super-block backups (for fsck -b #) at:
&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
- comes with &man.mdmfs.8; which automatically configures a
- &man.md.4; disk using &man.mdconfig.8;, puts a UFS file system
- on it using &man.newfs.8;, and mounts it using &man.mount.8;.
- For example, to create and mount the same file system image as
- above, type the following:</para>
-
- <example>
- <title>Configure and Mount a File-Backed Disk with
- <command>mdmfs</command></title>
+ <para>
+ To create a new file-backed memory disk, first allocate an
+ area of disk to use. This example creates an empty 5K file
+ named <filename>newimage</filename>:</para>
<screen>&prompt.root; <userinput>dd if=/dev/zero of=<replaceable>newimage</replaceable> bs=1k count=<replaceable>5</replaceable>k</userinput>
5120+0 records in
-5120+0 records out
-&prompt.root; <userinput>mdmfs -F <replaceable>newimage</replaceable> -s <replaceable>5</replaceable>m md<replaceable>0</replaceable> <replaceable>/mnt</replaceable></userinput>
-&prompt.root; <userinput>df <replaceable>/mnt</replaceable></userinput>
-Filesystem 1K-blocks Used Avail Capacity Mounted on
-/dev/md0 4718 4 4338 0% /mnt</screen>
- </example>
-
- <para>When <option>md</option> is used without a unit number,
- &man.mdmfs.8; uses the &man.md.4; auto-unit feature to
- automatically select an unused device. For more details
- about &man.mdmfs.8;, refer to its manual page.</para>
-
- <indexterm>
- <primary>disks</primary>
- <secondary>detaching a memory disk</secondary>
- </indexterm>
- <example>
- <title>Creating a New Memory-Based Disk with
- <command>mdmfs</command></title>
+5120+0 records out</screen>
- <screen>&prompt.root; <userinput>mdmfs -s <replaceable>5</replaceable>m md<replaceable>2</replaceable> <replaceable>/mnt</replaceable></userinput>
+ <para>Next, attach that file to a memory disk, label the memory
+ disk and format it with the <acronym>UFS</acronym> file
+ system, mount the memory disk, and verify the size of the
+ file-backed disk:</para>
+
+ <screen>&prompt.root; <userinput>mdconfig -f <replaceable>newimage</replaceable> -u <replaceable>0</replaceable></userinput>
+&prompt.root; <userinput>bsdlabel -w md<replaceable>0</replaceable> auto</userinput>
+&prompt.root; <userinput>newfs md<replaceable>0</replaceable>a</userinput>
+/dev/md0a: 5.0MB (10224 sectors) block size 16384, fragment size 2048
+ using 4 cylinder groups of 1.25MB, 80 blks, 192 inodes.
+super-block backups (for fsck -b #) at:
+ 160, 2720, 5280, 7840
+&prompt.root; <userinput>mount /dev/md<replaceable>0</replaceable>a <replaceable>/mnt</replaceable></userinput>
&prompt.root; <userinput>df <replaceable>/mnt</replaceable></userinput>
Filesystem 1K-blocks Used Avail Capacity Mounted on
-/dev/md2 4846 2 4458 0% /mnt</screen>
- </example>
+/dev/md0a 4710 4 4330 0% /mnt</screen>
+
+ <para>It takes several commands to create a file- or memory-backed file
+ system using <command>mdconfig</command>. &os; also
+ comes with <command>mdmfs</command> which automatically configures a
+ memory disk, formats it with the <acronym>UFS</acronym> file system,
+ and mounts it. For example, after creating
+ <replaceable>newimage</replaceable> with
+ <command>dd</command>, this one command is equivalent to
+ running the <command>bsdlabel</command>,
+ <command>newfs</command>, and <command>mount</command>
+ commands shown above:</para>
+
+ <screen>&prompt.root; <userinput>mdmfs -F <replaceable>newimage</replaceable> -s <replaceable>5</replaceable>m md<replaceable>0</replaceable> <replaceable>/mnt</replaceable></userinput></screen>
+
+ <para>To instead create a new memory-based memory disk with
+ <command>mdmfs</command>, use this one command:</para>
+
+ <screen>&prompt.root; <userinput>mdmfs -s <replaceable>5</replaceable>m md<replaceable>1</replaceable> <replaceable>/mnt</replaceable></userinput></screen>
+
+ <para>If the unit number is not specified,
+ <command>mdmfs</command> will
+ automatically select an unused memory device. For more details
+ about <command>mdmfs</command>, refer to &man.mdmfs.8;.</para>
</sect2>
</sect1>
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