Because I needed some tool to verify that the trouble at my side was not caused by a defective VDI file structure.

make
./vdicheck -v IMAGE.vdi

• Read the header of an VDI file and checks it for obvious magics.
• Read the gaps in the VDI file and look if they are filled with NUL
• Read the block chain and verify that it is correct
• Output some diagnostics, with -v also show empty fields
• If verification fails, program returns false

• Report bad alignments, the blocks should be alinged on 4K boundaries for modern SSD drives
• Grok others than the two type of VDI files I saw
• Make sense of the "unknown2" field, for now it just dumps it
• Make sense of all the other UUIDs
• Verify UUID chains (like snapshots or immutable disks)
• Repair defective block chains
• Defragment VDI files
• Align VDI files
• Convert dynamic VDI files into fixed and vice versa

• Some header fields are unclear to me as I did not dive into the VirtualBox source code yet. Also the code was only tested with the VDI files I had.