In a Previous “How To”, we discussed how to us a virtual hard drive to create a virtual machine to would run it. See “How to Configure A Virtual Machine in Windows 7.” In this final How To on the same subject we will discuss how to create a difference image from the existing vhd.
A difference file is an image, or snapshot of the main vhd. It is intended to allow the user to work with the image, and not worry about damaging the main vhd file. In other words, by using the difference file, the user can work and perform any tasks he wants and it will not impact the main vhd; indeed the image file can even be deleted, but the main vhd will still be there. Even so much as to recreate the difference file.
The steps to perform this are simple and straight forward.
For starters, let’s look at the folder that has the vhd and the vmc. We will create a new folder called Difference.
Create a New Folder - Difference
Next we will return to the Virtual PC Console. That is where we will create the difference file. Click Start
Select Start -> Microsoft Virtual PC
Virtual PC Console
From this we will go to the menu and select File
Then select Virtual Disk Wizard
Select the Virtual Disk Wizard
Welcome To The Virtual Disk Wizard
Click Next
Select Create a new virtual disk
Disk Options
Virtual Disk Type
Click Next
Here we will use the existing vhd and create a new one in the difference folder.
Click Browse
Virtual Hard Disk Location
First we identify the vhd file
Virtual Hard Disk Location - 2778.vhd
Select the 2778.vhd file and select Difference and open it.
Virtual Hard Disk Location Difference
Click save.
The Path for the Virtual Hard Disk location
Click Next
From the options select Differencing
Virtual Hard Disk Options - Differencing
Click next
Now you are asked to select the parent. This is the master vhd file on which the differencing (image) is created. So we must leave the Differencing folder and return to the previous folder that is resides in.
click Browse
Differencing Virtual Hard Disk - Name and Location-2778-VHD
Difference - No items match your search
Go up a level
Differencing Virtual Hard Disk - 2778.vhd
Select Open
Differencing Virtual Hard Disk - Name and Location-2778.VHD
Select Next
Completing the Virtual Disk Wizard - Finish
Click Finish
Virtual disk was created successfully
And this is what the vhd image will look like:
2778.vhd image
The vhd image file is in the difference folder. It has a size of only 21 KB. Compare this the vhd file of 6,393,989 KB. This is why it is considered a snapshot and will only retain information for the image, not the main vhd file.
The next to the last step is to copy the SQLServer-2005.vmd file to the Difference folder.
That part is easy, you will do a copy and paste operation. Select the file SQLServer-2005.vmc copy it and paste it over to Difference.
Copy SQLServer-2005-vmc
Copy SQLServer-2005-vmc To the Difference folder
Now launch the SQLServer-vmc file (click).
It will be put into the Virtual PC Console and run from there.
VirtualPC Console running the SQL Server 2005 vmc file
This was the third of a series of “How To” posts on using the Virtual Machine Console and creating vmc’s. Virtual machines are a computer running inside a computer. They are sandbox’s which allow users to work in a production environment, but without affecting that environment. They also save money by not having to buy additional hardware to run special applications. They can be run from inside a host machine.
