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MDCONFIG(8)			   BSD System Manager's Manual			      MDCONFIG(8)

NAME
     mdconfig -- configure and enable memory disks

SYNOPSIS
     mdconfig -a -t type [-n] [-o [no]option] ... [-f file] [-s size] [-S sectorsize] [-u unit]
	      [-x sectors/track] [-y heads/cyl]
     mdconfig -d -u unit [-o [no]force]
     mdconfig -l [-n] [-v] [-u unit]

DESCRIPTION
     The mdconfig utility configures and enables md(4) devices.

     Options indicate an action to be performed:

     -a      Attach a memory disk.  This will configure and attach a memory disk with the parame-
	     ters specified and attach it to the system.

     -d      Detach a memory disk from the system and release all resources.

     -t type
	     Select the type of the memory disk.

	     malloc   Storage for this type of memory disk is allocated with malloc(9).  This
		      limits the size to the malloc bucket limit in the kernel.  If the -o
		      reserve option is not set, creating and filling a large malloc-backed mem-
		      ory disk is a very easy way to panic a system.

	     vnode    A file specified with -f file becomes the backing store for this memory
		      disk.

	     swap     Storage for this type of memory disk is allocated from buffer memory.
		      Pages get pushed out to the swap when the system is under memory pressure,
		      otherwise they stay in the operating memory.  Using swap backing is gener-
		      ally preferable over malloc backing.

     -f file
	     Filename to use for the vnode type memory disk. Options -a and -t vnode are implied
	     if not specified.

     -l      List configured devices.  If given with -u, display details about that particular
	     device.  If -v option specified, show all details.

     -n      When printing md device names, print only the unit number without the md prefix.

     -s size
	     Size of the memory disk.  Size is the number of 512 byte sectors unless suffixed
	     with a b, k, m, g, or t which denotes byte, kilobyte, megabyte, gigabyte and ter-
	     abyte respectively. Options -a and -t swap are implied if not specified.

     -S sectorsize
	     Sectorsize to use for malloc backed device.

     -x sectors/track
	     See the description of the -y option below.

     -y heads/cylinder
	     For malloc or vnode backed devices, the -x and -y options can be used to specify a
	     synthetic geometry.  This is useful for constructing bootable images for later down-
	     load to other devices.

     -o [no]option
	     Set or reset options.

	     [no]async
		     For vnode backed devices: avoid IO_SYNC for increased performance but at the
		     risk of deadlocking the entire kernel.

	     [no]reserve
		     Allocate and reserve all needed storage from the start, rather than as
		     needed.

	     [no]cluster
		     Enable clustering on this disk.

	     [no]compress
		     Enable/Disable compression features to reduce memory usage.

	     [no]force
		     Disable/Enable extra sanity checks to prevent the user from doing something
		     that might adversely affect the system.

	     [no]readonly
		     Enable/Disable readonly mode.

     -u unit
	     Request a specific unit number for the md(4) device instead of automatic allocation.

EXAMPLES
     To create a 4 megabyte malloc(9) backed memory disk.  The name of the allocated unit will be
     output on stdout like ``md3'':

	   mdconfig -a -t malloc -s 4m

     To create a disk named /dev/md4 with /tmp/boot.flp as backing storage:

	   mdconfig -a -t vnode -f /tmp/boot.flp -u 4

     To detach and free all resources used by /dev/md4:

	   mdconfig -d -u 4

     To create a 128MByte swap backed disk, initialize an ffs(7) file system on it, and mount it
     on /tmp:

	   mdconfig -a -t swap -s 128M -u 10
	   newfs -U /dev/md10
	   mount /dev/md10 /tmp
	   chmod 1777 /tmp

     To create a 5MB file-backed disk (-a and -t vnode are implied):

	   dd if=/dev/zero of=somebackingfile bs=1k count=5k
	   mdconfig -f somebackingfile -u 0
	   bsdlabel -w md0 auto
	   newfs md0c
	   mount /dev/md0c /mnt

     To create an md(4) device out of an ISO 9660 CD image file (-a and -t vnode are implied),
     using the first available md(4) device, and then mount the new memory disk:

	   mount -t cd9660 /dev/`mdconfig -f cdimage.iso` /mnt

SEE ALSO
     md(4), ffs(7), bsdlabel(8), fdisk(8), mdmfs(8), malloc(9)

HISTORY
     The mdconfig utility first appeared in FreeBSD 5.0 as a cleaner replacement for the vn(4)
     and vnconfig(8) combo.

AUTHORS
     The mdconfig utility was written by Poul-Henning Kamp <phk@FreeBSD.org>.

BSD					  June 21, 2008 				      BSD
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