How to create VHD disk image from a Linux live system?

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Once more, I have to resort at the experts here at SuperUser, as my other sources (mainly Google ;-)) didn’t prove very helpful…

So basically, I would like to create a VHD image of a physical disk to be archived/accessed/maybe even mounted in a virtual machine.
Now, there are dozens of articles and tutorials on how to do that on the web, but none that meets exactly the conditions I would like to achieve:

  • I would like the destination file to be a VHD image, as Windows 7 can mount it natively, even over the network and many other programs can use it (VirtualBox, …)
  • The disk I’m trying to image contains a Windows XP install, so in theory, I could use the disk2vhd utility, but I would like to find a solution that doesn’t require booting that Windows XP install (ie keep the disk read-only)
  • Thus I was searching for a solution involving some sort of live system (running from a USB stic or the network)

However, all the solutions that I’ve came across either make use of disk2vhd or use the dd command under linux, which does a complete copy of the disk (ie even empty blocks) and does not output a VHD file. Is there a tool/program under Linux that can directly create a VHD file? Or is is possible to convert a raw disk image created using dd to a VHD file, without allocating space for the empty blocks? How would you proceed?

As always, any advice or comment is highly appreciated!!

Answer

For future reference, here is how I finally proceeded, with a few comments on the various issues or pitfalls encountered:

1. Boot the machine with a Linux live system

First step was to boot the machine containing the disk to image, using a Linux live system.

NOTE: My first idea was to use an Ubuntu Live USB disk, but the
machine did not support booting from USB, so I found it easier to use
an old Knoppix live CD.

2. Image the disk using dd and pipe the data through ssh

Then, I copied all the disk content to a file image on my local server using dd and piping the data through ssh:

$ dd if=/dev/hdX bs=4k conv=noerror,sync | ssh -c blowfish myuser@myserver ‘dd of=myfile.dd’

A few comments here: this method will read all the disk contents, so it can take very long (it took me 5hrs for a 80Gb disk). The bottleneck isn’t the network, but really the disk read speed. Before launching the copy, I advice to check the BIOS/disk/system parameters to ensure that the disk and the motherboard are working at their highest possible speed (this can be checked using the command hdparm -i and by running a test with hdparm -Tt /dev/hdX).

NOTE: dd does not output progress of the operation, but we can force it to do so by sending the USR1 signal to the dd process PID from another terminal:

$ kill -USR1 PIDofdd

Note: Newer versions of dd support the status=LEVEL option (man dd)

   status=LEVEL
          The  LEVEL of information to print to stderr; 'none' suppresses everything but error messages, 'noxfer' suppresses
          the final transfer statistics, 'progress' shows periodic transfer statistics

3. Reclaim the unused space

At this point, the source machine is no longer needed and we will work exclusively on the destination server (running Linux as well). VirtualBox will be used to convert the raw disk image to the VHD format, but before doing so, we can zero out the unused blocks, so that VirtualBox does not allocate space for them in the final file.

In order to do so, I mounted the images as a loopback device:

$ mount -o loop,rw,offset=26608813056 -t ntfs-3g /mnt/mydisk/myfile.dd /mnt/tmp_mnt
$ cat /dev/zero > zero.file
$ rm zero.file

NOTE: The offset indicating the beginning of the partition within the disk image can be obtained by using parted on the image file:

$ parted /mnt/mydisk/myfile.dd
(parted) unit
Unit?  [compact]? B
(parted) print
Model:  (file)
Disk /mnt/mydisk/myfile.dd: 80026361856B
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start         End           Size          Type      File system  Flags
 1      32256B        21936821759B  21936789504B  primary   ntfs         boot
 2      21936821760B  80023749119B  58086927360B  extended               lba
 5      26608813056B  80023749119B  53414936064B  logical   ntfs

NOTE2: The default Linux kernel NTFS driver provides read-only access, thus it is necessary to install and use the userspace ntfs-3g driver or writing to the disk will raise an error!

4. Create the VHD image using VBoxManage

At this point, we can use the VirtualBox utilities to convert the raw image to a VHD file:

VBoxManage convertfromraw myfile.dd myfile.vhd --format VHD

Attribution
Source : Link , Question Author : Federico , Answer Author : Android Control

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