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

NAME
     mdconfig — create and control memory disks

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

DESCRIPTION
     The mdconfig utility creates and controls 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 parameters specified and attach it to the system.
	     If the -u unit option is not provided, the newly created device
	     name will be printed on stdout.

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

     -r      Resize a memory disk.

     -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 memory
		     disk is a very easy way to panic the 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 swap when the
		     system is under memory pressure, otherwise they stay in
		     the operating memory.  Using swap backing is generally
		     preferred instead of using malloc backing.

	     null    Bitsink; all writes do nothing, all reads return zeroes.

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

     -l      List configured devices.  If given with -u, display details about
	     that particular device.  If given with -f file, display md(4)
	     device names of which file is used as the backing store.  If both
	     of -u and -f options are specified, display devices which match
	     the two conditions.  If the -v option is specified, show all
	     details.

     -n      When printing md(4) device names, print only the unit number
	     without the md(4) prefix.

     -s size
	     Size of the memory disk.  Size is the number of 512 byte sectors
	     unless suffixed with a b, k, m, g, t, or p which denotes byte,
	     kilobyte, megabyte, gigabyte, terabyte and petabyte respectively.
	     When used without the -r option, the -a and -t swap options are
	     implied if not specified.

     -S sectorsize
	     Sectorsize to use for the memory disk, in bytes.

     -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 con‐
	     structing bootable images for later download 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 sys‐
		     tem.  This can be used with the -d flag to forcibly
		     destroy an md(4) disk that is still in use.

	     [no]readonly
		     Enable/disable readonly mode.

     -u unit
	     Request a specific unit number or device name for the md(4)
	     device instead of automatic allocation.  If a device name is
	     specified, it must be start with “md” followed by the unit num‐
	     ber.

     The last form, mdconfig file, is provided for convenience as an abbrevia‐
     tion of mdconfig -a -t vnode -f file.

EXAMPLES
     Create a disk with /tmp/boot.flp as backing storage.  The name of the
     allocated unit will be printed on stdout, such as “md0”:

	   mdconfig /tmp/boot.flp

     Create a 1 gigabyte swap backed memory disk named “md3”:

	   mdconfig -s 1g -u md3

     Detach and free all resources used by /dev/md3:

	   mdconfig -du md3

     Show detailed information on current memory disks:

	   mdconfig -lv

     Resize the “md3” memory disk to 2 gigabytes:

	   mdconfig -rs 2g -u md3

     Create a 1 gigabyte swap backed disk, initialize an ffs(7) file system on
     it, and mount it on /tmp:

	   mdconfig -s 1g -u md10
	   newfs -U /dev/md10
	   mount /dev/md10 /tmp
	   chmod 1777 /tmp

     Create a memory disk out of an ISO 9660 CD image file, using the first
     available md(4) device, and then mount it:

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

     Create a file-backed device from a hard disk image that begins with 512K
     of raw header information.  gnop(8) is used to skip over the header
     information, positioning md1.nop to the start of the filesystem in the
     image.

	   mdconfig -u md1 -f diskimage.img
	   gnop create -o 512K md1
	   mount /dev/md1.nop /mnt

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

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

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

BSD			       October 10, 2015 			   BSD