- MDCONFIG(8) FreeBSD 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
- mdconfig -l [-n] [-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 parameters 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 memory
- disk is a very easy way to panic a system.
- vnode A file specified with -f file becomes the backingstore
- for this memory disk.
- swap Swap space is used to back this memory disk.
- -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.
- -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, kilo-
- byte, megabyte, gigabyte and terabyte 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 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.
- [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:
- 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 and mount a 128MByte swap backed file system 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
- SEE ALSO
- md(4), bsdlabel(8), fdisk(8), mdmfs(8), malloc(9)
- HISTORY
- The mdconfig utility first appeared in FreeBSD 7.0 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>.
- FreeBSD 7.2 November 6, 2010 FreeBSD 7.2
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