Date: Thu, 24 Apr 2014 18:24:48 +0000 (UTC) From: Dru Lavigne <dru@FreeBSD.org> To: doc-committers@freebsd.org, svn-doc-all@freebsd.org, svn-doc-head@freebsd.org Subject: svn commit: r44647 - head/en_US.ISO8859-1/books/handbook/disks Message-ID: <201404241824.s3OIOmvB070233@svn.freebsd.org>
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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>
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