http://forums.freebsd.org/showthread.php?t=20382

Create a virtual disk with a blocksize of 4096

% dd if=/dev/zero of=imageFile bs=4k count=<count of 4k blocks>

Create a file backed device

# mdconfig -a -t vnode -f imageFile -u 0

Now for the configuration of the geli(1) tool.

Fetch some random data to encrypt the master key with

# dd if=/dev/random of=/root/md0.key bs=64 count=1

Init the device with geli (question for passphrase here)

# geli init -s 4096 -K /root/md0.key /dev/md0

attach geli with the key to the newly created device

# geli attach -k /root/md0.key /dev/md0

This will create a device called /dev/md0.eli which is used in all

future commands.

Create a new filesystem on the virtual disk

# newfs /dev/md0.eli

Mount the disk

# mount /dev/md0.eli <mountpoint>

Now you can use the disk, do whatever you want with it.

To securely unmount the device

# umount <mountpoint>

# geli detach md0.eli

To restore from your metadata backups, for example if you accidentially

cleared the device with geli(1).

# geli restore /var/backups/md0.eli /dev/md0

Detach the memory disk completely from the system

# mdconfig -d -u 0

That's about it, with these simple commands you can create, encrypt and

use a virtual memory disk.

Here are two really simple shell scripts that will take care of mounting

and unmounting the created memory disks:

mountImage.sh

Code:

#!/bin/sh

# Basic script to mount memory disks

mountImage()

{

	dev=$1

	dir=$2

	echo "mounting $dev at $dir"

	mount $dev $dir

}

echo "Give me the name of the image to mount"

read image

echo "Where to mount it?"

read mountDir

echo "Where is the geli key?"

read geliKey

baseDevice="/dev/md"

# get the first free minor number to mount it to

for minorNumber in 0 1 2 3 4 5 6 7 8 9 10

do

	device=$baseDevice$minorNumber

	if [ -e $device ]

	then

	else

		echo "Found free device $device"

		break

	fi

done

echo "Using $device to mount $image"

mdconfig -a -t vnode -f $image -u $minorNumber

exitStatus=$?

if [ $exitStatus -eq 0 ]

then

	echo "Created $device from $image"

	geli attach -k $geliKey $device

	if [ $? -eq 0 ]

	then

		mountImage $device".eli" $mountDir

	fi

fi

and

umountImage.sh

Code:

#!/bin/sh

echo "What dir to unmount?"

read umountDir

echo "What device to detach with geli? (md0, md1, ...)"

read geliDevice

echo "Whats its minornumber? (0, 1, ...)"

read minor

umount $umountDir

device="/dev/"$geliDevice".eli"

if [ -e $device ]

then

	geli detach $device

	mdconfig -d -u $minor

fi