Archipelago » qemu

@subsection Raw disk images

The disk images can simply be raw images of the hard disk. You can

create them with the command:

dd of=myimage bs=1024 seek=mysize count=0

where @var{myimage} is the image filename and @var{mysize} is its size

in kilobytes.

write back to the raw disk images by pressing @key{C-a s}.

NOTE: The snapshot mode only works with raw disk images.

@subsection Copy On Write disk images

QEMU also supports user mode Linux

(@url{http://user-mode-linux.sourceforge.net/}) Copy On Write (COW)

disk images. The COW disk images are much smaller than normal images

as they store only modified sectors. They also permit the use of the

same disk image template for many users.

To create a COW disk images, use the command:

@example

qemu-mkcow -f myrawimage.bin mycowimage.cow

@end example

@file{myrawimage.bin} is a raw image you want to use as original disk

image. It will never be written to.

@file{mycowimage.cow} is the COW disk image which is created by

@code{qemu-mkcow}. You can use it directly with the @option{-hdx}

options. You must not modify the original raw disk image if you use

COW images, as COW images only store the modified sectors from the raw

disk image. QEMU stores the original raw disk image name and its

modified time in the COW disk image so that chances of mistakes are

reduced.

If the raw disk image is not read-only, by pressing @key{C-a s} you

can flush the COW disk image back into the raw disk image, as in

snapshot mode.

COW disk images can also be created without a corresponding raw disk

image. It is useful to have a big initial virtual disk image without

using much disk space. Use:

@example

qemu-mkcow mycowimage.cow 1024

@end example

to create a 1 gigabyte empty COW disk image.

NOTES: 

@enumerate

@item

COW disk images must be created on file systems supporting

@emph{holes} such as ext2 or ext3.

@item 

Since holes are used, the displayed size of the COW disk image is not

the real one. To know it, use the @code{ls -ls} command.

@end enumerate

@subsection Convert VMware disk images to raw disk images

You can use the tool @file{vmdk2raw} to convert VMware disk images to

raw disk images directly usable by QEMU. The syntax is:

@example

vmdk2raw vmware_image output_image

@end example