I *LOVE* the new boot from VHD feature in Win7. I am primarily using it for doing some VS 2010 dogfooding without messing up my primary drive partition. But man, the process for setting up a VHD for booting is brutal. Scott Hanselman did a great job laying out the steps, but I wanted something a bit more productive.
First, I created a clean Win7 RC VHD and zipped it up for easy storage. The basic Win7 RC VHD is just under 5GB, but compresses down to about 1.5GB with 7-zip. I used the ImageX process Aviraj described though in the future I’ll use the Install-WindowsImage script. Install-WindowsImage is more convenient to use because it will list the indexes within a given .wim file instead of making you grovel thru an XML file like ImageX does. Also Install-WindowsImage is 27k download while ImageX is part of the 1.4 gigabyte Windows Automated Installation Kit. Look, I’m not hurting for bandwidth, but I don’t see the point of downloading 54442 times more data for a utility that isn’t as useful.
Once you’ve created the VHD, you need to update your Boot Configuration Data, or BCD for short, using the appropriately named BCDEdit utility. The process is fairly straight forward, if tedious. You have to run BCDEdit four times, copy the configuration GUID to the clipboard and type out the path to the VHD in a slightly funky syntax. Blech. So I built a PowerShell script to automate updating the BCD, called add-bcd-vhd. You can get it from my skydrive. Pass in the name of the BCD entry and the path to the VHD and add-bcd-vhd will do the rest.
I was whining on Twitter yesterday that there’s no PowerShell specific tools for managing the BCD data. Add-bcd-vhd just runs bcdedit behind the scenes and processes the text output with regular expressions. Ugly, but effective. I decided to spend some time trying accessing the BCD data from its WMI provider, but that turned out to be way too much of a hassle to be effective. If someone else out there knows how to use the BCD WMI provider from PowerShell, I’d appreciate some sample code.