md(4)

NAME

md - memory disk

SYNOPSIS

device md

DESCRIPTION

The md driver provides support for four kinds of memory

backed virtual
disks:

malloc Backing store is allocated using malloc(9). Only

one malloc

bucket is used, which means that all md devices

with malloc
backing must share the malloc-per-bucket-quota.

The exact size
of this quota varies, in particular with the amount

of RAM in
the system. The exact value can be determined with

vmstat(8).

preload A file loaded by loader(8) with type `md_image' is

used for

backing store. For backwards compatibility the

type `mfs_root'
is also recognized. If the kernel is created with

option
MD_ROOT the first preloaded image found will become

the root
file system.

vnode A regular file is used as backing store. This al

lows for mount

ing ISO images without the tedious detour over ac

tual physical
media.

swap Backing store is allocated from swap space.

For more information, please see mdconfig(8).

SEE ALSO

disklabel(5), disklabel(8), fdisk(8), loader(8), mdcon

fig(8), mdmfs(8),
newfs(8), vmstat(8)

HISTORY

The md driver first appeared in FreeBSD 4.0 as a cleaner re

placement for
the MFS functionality previously used in PicoBSD and in the

FreeBSD
installation process.

The md driver did a hostile takeover of the vn(4) driver in

FreeBSD 5.0.

AUTHORS

The md driver was written by Poul-Henning Kamp <phk@FreeB

SD.org>.

BSD March 9, 2001

BSD