VDI
Also known as: .vdi file, VirtualBox Disk Image, virtual disk
VDI (VirtualBox Disk Image) is the native virtual hard-disk format for Oracle VirtualBox. A single .vdi file represents an entire virtual machine’s disk — its operating system, programs, and files — so it can be very large and grows as the VM is used.
- VirtualBox’s native virtual hard-disk format
- Holds an entire VM’s OS and files in one file
- Often dynamically growing and very large
What a VDI file contains
A .vdi file is a virtual hard drive: from inside the virtual machine it looks like a real disk, but on your host it is one big file. It holds the guest operating system and everything installed in the VM.
VDIs are usually dynamically allocated, meaning the file starts small and grows toward its maximum size as the VM stores more data. Deleting files inside the VM does not automatically shrink the .vdi on the host.
VDI vs VMDK/VHD and storage
VDI is specific to VirtualBox, much as VMDK is associated with VMware and VHD with Microsoft tools. VirtualBox can also use those formats, and disk images can often be converted between them.
Virtual-disk files are among the largest single files on a machine — easily tens of gigabytes. If you have stopped using a VM, deleting its .vdi reclaims real space; for one you keep, "compacting" the disk can recover space freed inside the guest.