virtualbox.org

Host: Debian Unstable
Guest: Debian Stable

I want to return to Debian Stable. My whole OS is placed on sda1. In order to make this transition smoother I created a VM containing Debian Stable installed on virtual sda1 of the same size as the real sda1 and tuned it. I plan to make dd image of virtual sda1 and then write it over of real sda1 that contains my current host system.

Now there is a problem, I don't know how to quickly make dd-image of virtual sda1. I tried to run Knoppix with Guest Addons in text-mode, but dd is working too slowly. For comparison , it takes about 10 minutes to make dd-image of real sda1.

Is there any way to speed things up? I have hunch that maybe the best way is to access virtual sda1 without running VM at all. I know that it's possible to mount VDI's, but in my case I need to access it as was raw /dev file.

dd is slow, be very patient. You can change the block size to speed things up a little. There are a number of things that happen though, smaller disks dd slower than large disks due to the position of the bits on the disk (larger disks require less revolutions to copy same amount of data), not that they are different in diameter, but compression for lack of better terms. Changing the block size to larger isn't always best option for dd'ing a complete install, for best results stick with the bs shown in: whereas X is the disk of interest. Remember it has to be dd'd from beginning of disk to get the boot sector - as a safe measure might consider dd'ing an img of the boot sector as a backup.
dd when you can afford 10 hours. There are some other tools available for converting vm's to iso's or img's for installing on metal - check the clonevdi blogs for one, and VBoxManage has some operands.