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FreeBSD 11.0 - man page for mdconfig (freebsd section 8)

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

     mdconfig -- configure and enable memory disks

     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

     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.  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 lim-
		     its 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 a system.

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

	     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 pre-
		     ferred 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) pre-

     -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.  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 constructing bootable images for later down-
	     load to other devices.

     -o [no]option
	     Set or reset options.

		     For vnode backed devices: avoid IO_SYNC for increased performance but at the
		     risk of deadlocking the entire kernel.

		     Allocate and reserve all needed storage from the start, rather than as

		     Enable clustering on this disk.

		     Enable/disable compression features to reduce memory usage.

		     Disable/enable extra sanity checks to prevent the user from doing something
		     that might adversely affect the system.

		     Enable/disable readonly mode.

     -u unit
	     Request a specific unit number or device name for the md(4) device instead of auto-
	     matic allocation.	If a device name is specified, it must be start with ``md'' fol-
	     lowed by the unit number.

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

     Create a 4 megabyte malloc(9) backed memory disk.	The name of the allocated unit will be
     printed on stdout, such as ``md3'':

	   mdconfig -a -t malloc -s 4m

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

	   mdconfig -a -t vnode -f /tmp/boot.flp -u md4

     Detach and free all resources used by /dev/md4:

	   mdconfig -d -u md4

     Create a 128MByte swap backed disk, initialize an ffs(7) file system on it, and mount it on

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

     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 md0
	   bsdlabel -w md0 auto
	   newfs md0c
	   mount /dev/md0c /mnt

     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

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

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

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

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

BSD					November 30, 2013				      BSD
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