Supported formats and file systems
Image formats
Every format below is both read and written. In the application window a trimmed image keeps its format; the command line tool can also write it in another one.
| Format | Used by | Notes |
|---|---|---|
| VHDX | Hyper-V | Dynamic and fixed disks. The trimmed image is always dynamic. |
| VHD | Hyper-V, Virtual PC, Azure | Dynamic and fixed disks. |
| VMDK | VMware, VirtualBox | Sparse disks in one file, and disks split into pieces with a descriptor file. A split disk stays split. Disks with a separate flat data file, as ESXi and preallocated VMware disks have, and stream-optimised disks are not supported yet. |
| VDI | VirtualBox | Differencing and undo disks are not supported. |
| qcow2 | QEMU, KVM, Proxmox | Versions 2 and 3. Compressed images, as cloud images are usually distributed, must be converted with qemu-img convert first. |
| Raw | Any | Files named .img, .raw, .dd or .bin. A trimmed raw image is a sparse file of the same length that takes less room on the disk, so it needs a host file system that supports sparse files. |
Snapshot and differencing disks and encrypted images are not trimmed. A base disk that snapshots or linked clones still depend on looks like any other disk and is not detected, so leave it alone.
Guest file systems
Disks partitioned with MBR or GPT, and disks holding a single file system with no partition table, are understood.
| File system | Free space reclaimed | Page, swap and hibernation files |
|---|---|---|
| NTFS | Yes | Yes |
| FAT12, FAT16, FAT32, exFAT | Yes | Yes |
| ext2, ext3, ext4 | Yes | Swap files |
| XFS | Yes | No |
| btrfs (single device) | Yes | No |
| APFS | Yes | No |
| HFS+ | Yes | Sleep image and swap files |
| Linux swap partition | Kept as it is | Yes |
| LVM, linear and thin volumes | The file systems inside the logical volumes are handled as above. | |
A volume whose file system is not in this list, for instance ReFS or ZFS, is copied to the trimmed image exactly as it is and shown as File system not recognised. So is an encrypted volume, which is shown as Encrypted: its free space cannot be seen from outside. The rest of the disk is trimmed as usual.