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Library - Xen - How-to - Disk images

Modern CD-ROM software can be used to read a CD-ROM (or DVD-ROM) and write the entire contents to a new .ISO file.  In your DomU, you will boot from this .ISO file as if it were a CD-ROM (only access will be much faster because hard drives, especially with NetBSD 5's caching, will always outperform physical CDs and DVDs).

Obtain or Create the .ISO file

For ReactOS users, simply downloading a recent .ISO file from the ReactOS web site ( will suffice.  We recommending renaming it to "reactos.iso" if you don't have any preferences.  At the time of this writing, ReactOS is nearing the end of the ALPHA development stage and we sincerely hope to see it in BETA sometime in the year 2009.

For Windows XP users, if you can borrow an installation CD that comes with Service Pack 3, your Product Key (the serial number required in order to install it) should work correctly with it.  You MUST have a genuine license for it, and that license MUST NOT be installed on any other computers, before you use it.

Create the virtual hard disk

Next, create a raw binary file for your DomU's 30 GB virtual hard drive using the following command, which will provide regular screen updates for your convenience:

dd if=/dev/zero of=/usr/pkg/etc/xen/images/win32-drive-c.bin bs=1m count=30720 progress=32

Change the "count" value to 10240 for 10 GBs, 20480 for 20 GBs, 40960 for 40 GBs, etc.

On our systems (which are made of high quality components including Intel CPUs, Intel motherboards with on-board SATA controllers, Seagate ES SATA hard drives, etc.), this completes in just over 6 minutes.  Depending on the quality of your hardware, its configuration, and many other factors, your results may not be the same (one Linux user reported that this "dd" command required more than 3 hours to complete; we don't know what their hardware specifications were).

Xen also supports a qemu feature, .qcow files, but this is beyond the scope of this document.  The reason we mention it is not only to highlight one more feature of Xen, but to also point out that you should, in theory, be able to take a pre-existing qemu hard drive and use it in an HVM in Xen (there might be some differences detected with hardware, so be sure to test with a duplicate of your qemu disk image).

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