Demo Tip: Using Differencing Disks to save hard drive space

If you are like me, you probably have a half a dozen or more active clients / prospects you are working with at any given time. Take that and times it by 9 GB each and you may have 10-20 of them on your machine at any given time. So running out of space is a real concern. (I have a main 300 GB Hard Drive, a backup 150GB and a secondary 40 GB and a back up to the secondary at 80 GB. And yes I run out of space on a regular basis. Mainly because I refuse to throw stuff away. J)

I also end up sharing disks with partners all the time. So I will do some customizations, the partner will add some data and a third partner may do some BI work on the image. Moving 10-12 GB across USB hard drives takes several hours to do and is something I don’t like doing. J

So I have been using differencing disks. What a differencing disk does is just capture the differences between the base image and the changes you made. So all your changes are store in a file that will be much smaller than the original image.

Another cool thing about differencing disks is that you can stagger them. So if an ISV makes a differencing disk, you can put the base image, the ISV differencing disk and then your customizations in a separate diff disk. So you would end up with something that looks like this:

Now there is a caveat. Your base image cannot change between machines. (So if you change your base and then do a diff disk, you would need to provide the diff disk and the base disk to the second machine.) So what I do is extract my base image and then turn it to READ ONLY immediately. It stops me from doing something stupid like changing my base disk and then creating diff disks or worse, changing the base and then the diff disks I have created won’t work at all. L

Differencing disks also work in Virtual Server. I have made the switch from Virtual PC to Virtual Server and it has been working well for me. I miss Shared Folders and dragging and dropping, but everything else is there and the level of control I have is much higher. (Yeah, so unless you are a control freak, stay with VPC.) The directions are a little different, but the disks created with Virtual PC can be used with Virtual Server and vice versa.

So how do you build a diff disk? Follow these simple steps.

1. Turn your Base (or VPC calls it a parent disk) to Read Only. (And do this BEFORE you turn on the Base drive for the first time.)

2. Start the VPC Console

3. File | New Disk Wizard

4. Select Create a New Virtual Disk

5. Select a New virtual hard disk

6. Give your Disk a name (On your compressed external hard drive… J)

7. Select Differencing Disk

8. Select the “Parent” disk or the one called CRM.VHD that you unzipped from the package you downloaded. (The one you turned to Read Only in the first step.)

9. Create a new VPC using the Hard Drive you just created

10. The new differencing disk should be about 3GB or so with a bunch of customizations made to it.

Now just add a new Virtual machine and select the hard drive you have created above as your main hard drive. J

Happy Demos!