Monday, September 19, 2011

Enhanced VMDK support now in QEMU

QEMU now has greatly enhanced VMDK VMware disk image file support, thanks to Fam Zheng's hard work during Google Summer of Code 2011. Previously QEMU was only able to handle older VMDK files because it did not support the entire VMDK file format specification. This resulted in qemu-img convert and other tools being unable to open certain VMDK files. As of now, qemu.git has merged code to handle the VMDK specification and work well with modern image files.

If you had trouble in the past manipulating VMDK files with qemu-img, it may be worth another look soon. You can already build the latest and greatest qemu-img from the qemu.git repository and distros will provide packages with full VMDK support in the future:

$ git clone git://
$ cd qemu
$ ./configure
$ make qemu-img
$ ./qemu-img convert ...

It is still recommended to convert VMDK files to QEMU's native formats (raw, qcow2, or qed) in order to get optimal performance for running VMs.

At the end of Fam's Summer of Code project, he put together an article on gotchas and undocumented behavior in the VMDK specification. This will be of great interest to developers writing their own code to manipulate VMDK image files. His experience this summer involved testing a wide range of VMware software, real-world image files, as well as studying existing open-source VMDK code. The VMDK specification is ambiguous in places and does not cover several essential details, so Fam had to figure them out himself and he then documented them.

So with that, happy VMDK-ing...