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Query about Diff Disk

Jan 8, 2010 at 4:07 PM

I would like to create a base / parent image and then have multiple children / differencing disks point to it.
the idea here is that when I then update the parent disk, all the child disks will
show the updated content.
Is this possible with the DiscUtils API and if so can someone please suggest a way to achieve it
Say the base / parent image has a single folder called C:\Folder1.

Let's say child one has a folder called C:\Child-Folder1
when we load up the child (VHD, VMDK) image, we will see C:\Folder1 and C:\Child-Folder1
Now say I add a new folder to the parent called C:\Folder2
when I load up the child I would like to display  C:\Folder1,  C:\Child-Folder1 and C:\Folder2
However this is not what I currently observe. After I add the new folder to the base/parent  image,  I still only see C:\Folder1,  C:\Child-Folder1.

If anybody  know then plz suggest me ..?


Jan 9, 2010 at 9:57 AM

Hi Rajesh,

Unfortunately, differencing disks don't work that way.  Differencing disks store disk sectors, not the file structure - so if you modify the parent disk, you'll experience what you've described and/or end up with a corrupt file system in the differencing disks.

In your example, there will be a single sector in the file system that contains the contents of the root directory.  When you create the C:\Child-Folder1, you end up with a copy of that sector in the differencing disk, so that no changes to that same sector in the parent disk will be visible.  So, when you then add a folder in the parent image you still see just two folders in the root of the virtual disk.