Portable bare metal backup and recovery for Windows — no agent, no driver, no service.
MjolnirVSS images a whole Windows system disk while Windows is running, and writes that image back onto a blank replacement disk after the original has failed. One executable, run from a folder. Delete the folder and nothing of it remains.
| Version | 0.1.0-alpha.2 — see CHANGELOG.md |
| Download | v0.1.0-alpha.2, a portable folder for 64 bit Windows, or build it yourself |
| Tested end to end | Backup, verify, restore and boot, on Windows 10, Windows 11, Server 2019 and Server 2025 |
| Licence | GPL-3.0-or-later |
Windows 10 22H2, Windows 11 24H2, Server 2019 and Server 2025 have each been
backed up live, verified, restored onto a blank disk from the recovery wizard,
and started unaided. Each restored machine matched 12 of 12 file hashes and kept
every partition's identifier, offset and size. The test environments and what
was measured in each are recorded in docs/testing.md.
MjolnirVSS is early alpha. Hardware configurations vary: test recovery in your own environment before relying on any backup tool, and keep the backup you already have until you have.
MjolnirVSS takes a deliberately portable approach: no installed service, no driver, no scheduled task and no runtime dependency, so the tool you rely on in an emergency is a folder you can carry.
- Nothing is installed. No service, no driver, no scheduled task, no registry entries, no runtime. It runs from a USB stick and leaves no trace.
- The image is of the whole disk, not a file selection. Partition table, EFI, Microsoft Reserved, Windows and recovery. If a partition needed to boot cannot be read, the backup fails rather than producing a disk that will not start.
- Free space is skipped. Only the clusters NTFS reports in use are read, so a 62.8 GiB partition holding 14.2 GiB is read in minutes, not hours.
- Every backup is verified as it is made. Each block is read back, decompressed and compared against its BLAKE3 digest before the backup is marked complete.
- The format is documented, not proprietary. A backup is a folder of JSON and
compressed blocks, specified in
docs/backup-format.mdin enough detail to write an independent reader. - It does not disturb other backup software. MjolnirVSS declares a copy
backup (
VSS_BT_COPY), so it does not move SQL Server's differential base and does not truncate Exchange's logs.
| Capability | State |
|---|---|
| Live backup of a running system through VSS | Working |
| Capturing the GPT layout, EFI, MSR, Windows and recovery partitions | Working |
| Used block imaging, skipping NTFS free space | Working |
| Verification of every block, on write and on demand | Working, including against deliberately damaged backups |
| Restore onto a blank disk, the same size or larger | Working |
| Rebuilding the partition table, checked partition by partition | Working |
| UEFI boot repair after a restore | Working; a deliberately broken disk was made to start again |
| Booting the restored Windows | Working on every version tested |
| Refusing unsafe restore targets | Working |
| Single file recovery out of a backup | Working |
| Recovery media built from this machine's own Windows recovery files | Working; the media it produces has been booted |
| Graphical backup window | Working |
| Graphical recovery wizard, operable from the keyboard alone | Working, driven through a whole restore with no mouse |
| Cancelling cleanly with Ctrl+C | Working; exits 9 cancelled and releases the shadow copy it held |
| Encrypted backups (Argon2id, AES-256-GCM) | Working; command line only, not yet offered in the window |
| BitLocker: unlocked volume backed up through its shadow copy | Working |
| BitLocker: locked volume | Refused, with an explanation |
| Restore point warning before a backup | Working |
| Incremental backups | Not implemented |
How each of these was exercised, and in what environment, is recorded in
docs/testing.md and
docs/vm-testing.md.
Download v0.1.0-alpha.2, unpack it anywhere, and run it. Nothing is installed. A SHA-256 sum is published beside the archive, so you can check that what you downloaded is what was built:
(Get-FileHash .\MjolnirVSS-0.1.0-alpha.2-windows-x64.zip -Algorithm SHA256).HashMjolnirVSS.exe inspect # what would be copied
MjolnirVSS.exe backup --destination E:\Backups # copy it
MjolnirVSS.exe verify E:\Backups\PC_2026-09-14_1015
MjolnirVSS.exe recovery-media --iso E:\Recovery.iso # make the rescue mediaOr run MjolnirVSS.exe with no arguments for the window. Both use the same
engine, so a bug found in one is the bug the other would have had.
Every backup verifies itself before it is marked complete, and the result says so rather than leaving you to wonder.
The backup lands in a folder named after the computer and the time, for example
DESKTOP-1A2B_2026-09-14_1015. --preview <bytes> captures only the first part
of each partition so the whole pipeline can be exercised in seconds; a preview
backup is marked as such and can never be restored.
- Windows 10, Windows 11 or Windows Server, 64 bit. Windows 10 22H2, Windows 11 24H2, Server 2019 and Server 2025 have each been backed up, restored and booted
- A UEFI machine with a GPT system disk
- One physical disk holding Windows
- An external NTFS drive with room for the backup
- Administrator rights, requested at start
Refused with an explanation rather than attempted: dynamic disks, Storage Spaces, software RAID, ReFS system volumes, legacy BIOS boot, Windows spread across several disks, and disks with an untested sector size.
Two behaviours worth knowing before the first run:
- Restore points. Windows keeps a volume's shadow copies in one pool and can
only release space from the oldest end, so removing the snapshot MjolnirVSS
took can cost you older restore points. This happens to any program that takes
a snapshot. MjolnirVSS deletes only its own snapshot, by identifier, and warns
before starting when there is anything to lose. Your files are unaffected.
docs/vss-lifecycle.md - BitLocker. An unlocked volume is read through its shadow copy, which
presents it decrypted, so the backup contains readable copies of your files
unless you pass
--encrypt. A restored disk comes back unencrypted; turn BitLocker on again afterwards. A locked volume is refused. MjolnirVSS never reads, stores or logs a recovery key.docs/bitlocker.md
Make the media while the computer still works. A computer that will not start cannot build its own rescue disc.
MjolnirVSS.exe recovery-media --iso E:\MjolnirVSS-Recovery.isoThe media is built from the Windows recovery files already on the machine —
nothing belonging to Microsoft is shipped or downloaded. It needs the Windows
ADK. docs/recovery-media.md
When the disk has failed, boot that media and the wizard starts on its own. It runs from the keyboard alone, which matters on a machine whose mouse may not be the thing that still works.
The drive holding the backup cannot be chosen. Before anything is erased you are
shown the target disk's number, model, serial number, size and current
partitions, and you have to type ERASE <serial number> exactly — y is not
accepted.
A disk too small for the layout is refused, every stored block is confirmed present before anything is erased, and the restore stops if the disk changed size between being checked and being written.
Single files can be recovered without restoring a machine: Restore files in
the window, or volumes / browse / extract on the command line. The backup
is opened read only; nothing is mounted and nothing is erased.
docs/file-recovery.md
Full walkthrough: docs/bare-metal-restore.md.
Every command takes --json and prints one document on standard output —
failures included, with the exit code inside it. Progress goes to standard
error and never pollutes the JSON. Nothing stops to ask a question: a command
that would otherwise have to ask refuses and names the flag rather than hanging.
$out = MjolnirVSS.exe --json list E:\Backups
$code = $LASTEXITCODE
if ($code -ne 0) { throw ($out | ConvertFrom-Json).error.what }Exit codes are a contract: 0 worked, 6 the backup is damaged, 7 the
destination is wrong, 9 cancelled, and so on. MjolnirVSS never registers a
scheduled task; create one yourself and point it at backup. The full table of
eleven codes, the failure document and a complete scheduled backup are in
docs/automation.md.
| Document | What it covers |
|---|---|
docs/architecture.md |
How the pieces fit together and why |
docs/backup-format.md |
The on disk format, in enough detail to reimplement |
docs/bare-metal-restore.md |
Recovering a computer, step by step |
docs/recovery-media.md |
Making bootable media from this machine's own Windows parts |
docs/file-recovery.md |
Getting single files back out of a backup |
docs/automation.md |
Exit codes, JSON output, scheduled backups |
docs/supported-configurations.md |
Exactly what is supported and what is refused |
docs/vss-lifecycle.md |
How the shadow copy is taken and released |
docs/bitlocker.md |
How BitLocker is handled, and the measurement behind it |
docs/encryption.md |
Encrypting a backup, what it hides and what it does not |
docs/threat-model.md |
What is treated as hostile, and what is not defended against |
docs/testing.md |
The test matrix, and what was virtual versus physical |
docs/vm-testing.md |
The virtual machine harness that proves the whole cycle |
docs/roadmap.md |
What comes next, in order |
Needs the stable Rust toolchain and the Visual Studio C++ build tools.
rustup target add x86_64-pc-windows-msvc
cargo build --release --workspace
cargo test --workspace
.\scripts\package.ps1package.ps1 produces dist\MjolnirVSS, the portable folder. It also checks
that the recovery executable does not import vssapi.dll, because that library
does not exist in Windows PE. The release build links the C runtime statically,
so the Visual C++ Redistributable is not required.
MjolnirVSS got its name from my fondness for Brothers of Metal, a Swedish metal band I listen to a lot. Their Norse mythology theme led to Mjölnir — Thor's hammer — and the name stuck for a tool built around getting a Windows machine back after a hard hit.
The VSS is the Volume Shadow Copy Service, which is the part of Windows that makes copying a running disk possible at all.
GPL-3.0-or-later. See LICENSE.
MjolnirVSS is an independent, clean room implementation. It is not derived from, and does not interoperate with, any commercial backup product. It uses documented Microsoft interfaces and a backup format designed for this project.