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
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, kilobyte, 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 constructing 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 system.
[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
