[vbox-dev] programatically created differencing disks

Geoff Nordli geoffn at gnaa.net
Mon Sep 28 17:07:12 PDT 2009


I am trying to build a “differencing” disk system that has a parent disk
which is read-only and then programmatically create a differencing disk from
the parent.  Similar to how Virtual PC and VMware work. 

I am looking at two different options:

1) A “snapshot” is really is differencing disk.  There is an option in the
GUI to "Show differencing disks" so it seems there may be a path to leverage
this functionality to create a snapshot and then to use this as a basis as a
template.  Maybe this could be used in combination with "2)".   

2) Use empty dynamic VDI files and then try to link them to the parent.  How
does vbox manage the linking?  Is there some information in the file header
telling it where the parent is located?  I opened one up, but nothing
obvious jumped out at me.

Any suggestions on these options? 

Ideally, we would be able to support “nested” differencing disks, where you
could have two or three disks linked to each to each other.  Anyone know if
this feature is on the roadmap?



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