MDCONFIG(8) 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 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 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 generally 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, 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 per- formance 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 au- tomatic allocation. EXAMPLES To create a 4 megabyte malloc(9) backed memory disk. The name of the allo- cated 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>. FreeBSD 8.2 June 21, 2008 MDCONFIG(8)
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