In my last post, Hummingboard: Giving Raspberry Pi a run for less money, I mentioned using a free. open source Windows utility called Win32 Disk Imager to create a disk image of Debian GNU/Linux “Jessie” on a micro SD card.
I was just asked to explain what's involved in disk imaging and how to do it on other operating systems, so, here goes …
What I was creating was a bootable disk from a “boot image”, that is, a disk image with a boot loader. Boot images are useful for archiving, backing up, duplicating, and restoring systems and can be used to create virtual machines from physical machines.
To create a disk image (whether bootable or not) you need a disk on which whatever content you want in the image has been set up and a disk imaging utility. The utility performs a block-by-block copy of the disk to a file. Beyond this basic operation there are many other features you might want. For example, some disk imagers can image open files, create disk images in multiple formats, verify and or encrypt images, and, crucially, restore to different hardware.
Disk images come in many formats including:
- VMDK, VHD, or VDI for virtual machines
- IMG and ISO are raw block level copies
- DMG, Apple’s disk image format (also a raw block level copy)
Unfortunately many of these file format names are interchangeable (for example Apple’s DMG format is sometimes given an IMG extension).
Win32 Disk Imager is one of the simplest tools for reading and writing disk images but only to and from USB drives and only with IMG formatted images. If you want more features, more media, and more flexibility but still also free then check out:
- Macrium Reflect Free (Windows)
- AOMEI Backupper Standard 2.0 (Windows)
- Clonezilla (Windows, Linux, OS X)
- SuperDuper (OS X)
This is just a small selection of what's available for free and most of these tools have premium upgrades that add in features such as scheduling.
For creating VMware compatible virtual machines from physical ones and vice versa, check out the free, open source VMware vCenter Converter Standalone.
If you have any other disk imaging tools you'd recommend, let me know ...