I am using virtualbox to test software on various linux distributions. The base Application (10-20GB CAE Suite) is stored on separate vdi, so I can have one vdi per Version of the Application and attach them to multiple virtual machines. These vdi are dynamically allocated and multiattach. Now I want to make a change, so that different versions of the CAE Suite use no extra space for identical data. Let's say I have V1 on v1.vdi and V2 on v2.vdi. They're similar enough, that say 50% of the data is the same. v2.vdi would refer to v1.vdi in the same or similar way as the drives on the various machines refer to the same base image using the multiattach feature.

I think there is some differential storage, which I want to employ. I cannot find the settings in the virtual media manager, that allow me to do this. I am willing to do this on the command line, but couldn't find it either. Host System is Windows.

migrated from stackoverflow.com May 21 '17 at 10:36

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A partial solution:

Simply adding the same vdi a second time to the same guest will generate a second differential medium in the virtual media manager. In the guest this looks like a copy, that I can edit (eg. starting changing the label and blkid).

This is fine, when I want this device attached to only one guest.

If I do the same on a second guest, I will get yet another differential medium. I have to make the same changes to this one. If the differential media are not shared among the guests, the benefit of saving space between the different versions of the CAE Suite are outweight by the duplication of the differential images for each guest.

So it would probably work for a very small number of guests compared to a large number of versions.

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