VM DISKFULL - use Snapshots as backup

[mpack]

That error (the wording had an original meaning which is now obscure), essentially means that you don't have the complete chain of snapshot files.

A snapshot chain consists of the base VDI, then the first snapshot you created, then the second snapshot you created, and so on until we reach the most recent snapshot you created.

Snapshot files are NOT stand alone, they are difference files, i.e. each file contains only the changes needed to patch the previous member of the chain to make this one. You need a complete chain to make one usable disk image.

To clone a snapshot with CloneVDI you copy all the VDIs (including the base) into one folder and then choose one of the snapshots. CloneVDI will use the snapshot header to find out which other VDI is the immediate parent of the selected snapshot. Then it will find the immediate parent of that snapshot, and so on until it finds the base VDI. Obviously you would ideally want to open the newest snapshot, as that will contain the most current data.

If CloneVDI is unable to find all of the members of a chain then you will get that "sorry, source is a difference image" error message, because the chain is incomplete and it therefore can't construct a usable disk image.


To overcome this error try examining the snapshot VDI header ("Header info..." is a button in CloneVDI) and notice the UUID parent info. That tells you who the parent is, so repeat on the parent. Eventually you'll find that one or more links are missing from the chain. You need to replace the missing files from a real backup, or else you must choose an earlier snapshot in CloneVDI, i.e. a shorter, older chain which can be traced all the way back to the base VDI. That will be the most recent disk image you can clone.

[alexisleroy]

Ok, thank you for your answer.

If I try to examining the snapshot VDI by checking the header, I have:
* {9819948a-d697-4f0d-bc11-4dfa5250ae4d}.vdi => UUID (parent): {009dd2a5-e0b6-4928-85c9-63b184d29b74}.vdi
* {009dd2a5-e0b6-4928-85c9-63b184d29b74}.vdi => UUID (parent): {638538e8-....} which I don't find in my Snapshots folder

So now I am going to install a brand new virtual machine with:
* VirtualBox-6.1.18-142142-Win.exe
* linuxmint-20.1-mate-64bit.iso

Thanks for your help