Snapshots Are Not Backups (and Other Things Rover Buried in the Yard)

Woof! It's Rover here. BOB said I could write this one, because I know a lot about burying things and digging them back up.

In a home lab, you will break things. That's the fun part! The less fun part is when you break something and can't un-break it. Proxmox gives you two ways to dig your way back: snapshots and backups. They sound alike, but they're as different as a chew toy and a bone. Let's sniff them out.

Snapshot vs. Backup

The short version: a snapshot is a bookmark, a backup is a spare copy of the book. If your house floods, the bookmark doesn't help much.

Snapshots: The Save Point

Before you try something scary (a big update, a registry hack, a "quick" config change), take a snapshot:

• In the web interface: select the VM → Snapshots → Take Snapshot.
• Check Include RAM to save the running memory too. Rolling back then puts the VM exactly where it was, still running. Leave it unchecked for a smaller, faster snapshot that rolls back to a "powered off" state.

Or from the host shell:

qm snapshot 105 before-update --description "Before the big update"   # take one
qm listsnapshot 105                                                    # list them
qm rollback 105 before-update                                          # go back in time
qm delsnapshot 105 before-update                                       # clean up

⚠️ Heads up: Snapshots need storage that supports them: ZFS, LVM-thin, Ceph, or qcow2 disk files. Plain LVM and raw files on a directory don't. If the Take Snapshot button is grayed out, that's usually why.

💡 Rover's tip: Don't leave snapshots lying around like old tennis balls. They slowly grow as the VM changes, take up space, and on some storage types they slow the disk down. Take one, do the risky thing, then delete it once you're happy.

Backups: The Spare Copy

Proxmox's built-in backup tool is called vzdump. It copies the whole VM (configuration and disks) into a single backup on whatever storage you point it at.

It has three modes:

For almost every lab VM, Snapshot mode plus the QEMU Guest Agent is the right choice. (BOB's article on Windows VMs covers installing the agent.)

Schedule it

Go to Datacenter → Backup → Add:

1. Storage: pick somewhere that isn't your VM disk. A USB drive, a NAS share (NFS or SMB), or Proxmox Backup Server.
2. Schedule: something like sun 02:00 or daily 03:00.
3. Selection: all VMs, or just the ones you care about.
4. Mode: Snapshot.
5. Retention: how many to keep. A friendly lab setting is keep-daily 7, keep-weekly 4, keep-monthly 3. That gives you about three months of history without filling the disk.

Run one by hand once with Run now, so you know it works before you need it.

Proxmox Backup Server: The Fancy Doghouse

Proxmox Backup Server (PBS) is a free companion product that's built for storing Proxmox backups. You can run it on a spare PC, a small VM on another machine, or even alongside a NAS.

Why people love it:

• Deduplication. The same data is only stored once. Twenty Windows VMs share a lot of the same files, so they take up far less space.
• Incremental backups. After the first backup, Proxmox tracks which blocks changed (with "dirty bitmaps") and only sends those. Nightly backups that took 20 minutes now take seconds.
• Verification. PBS can re-read backups on a schedule and check that they're still intact.
• File-level restore. Grab one file out of a backup without restoring the whole VM.

Domain Controllers and Time Travel

Rolling back a domain controller is like digging up a bone you already ate. Other DCs remember things your old DC doesn't, and Active Directory can get very confused (the scary name for this is USN rollback).

Good news: Windows Server 2012 and later domain controllers watch for a VM-Generation ID. When a hypervisor that supports it restores a snapshot, the ID changes, and the DC notices and protects itself. Proxmox supports this with the vmgenid setting, which new VMs get automatically.

Still, a few rules keep things calm:

• If you have one domain controller, snapshots and backups are fine. There's nobody else to disagree with it.
• If you have two or more, prefer restoring from a proper backup, and avoid rolling back just one DC to last month.
• Keep the clocks right. Restored VMs can come back with an old time.

The Golden Rule: Test Your Restores

A backup you've never restored is just a hopeful file. Once in a while:

1. Pick a backup.
2. Restore it to a new VM ID (so you don't overwrite the real one).
3. Disconnect its network, boot it, and check that it works.
4. Delete the test VM.

If that works, you've got real backups. If not, better to find out on a quiet Sunday than on the day the SSD goes pop.

💡 Rover's tip: The classic 3-2-1 rule works for labs too: 3 copies of your data, on 2 different kinds of storage, with 1 copy somewhere else (another building, or the cloud). Even "1 copy on a USB drive in a drawer" is a big step up from zero.

Wrapping Up

• Snapshots are quick save points on the same storage. Use them before risky changes, then delete them.
• Backups are full copies on different storage. Schedule them with retention.
• Use Snapshot mode plus the guest agent for no-downtime, consistent Windows backups.
• Proxmox Backup Server adds deduplication, fast incrementals and verification.
• Be gentle with domain controller rollbacks.
• Test your restores!

Now if you'll excuse me, I have some bones to back up.

Woof! See you next time!

— Rover 🐕

Sources

• Proxmox VE Administration Guide: Backup and Restore
• Proxmox VE Administration Guide: QEMU/KVM Virtual Machines (snapshots, VM Generation ID)
• Proxmox VE wiki: Storage
• Proxmox Backup Server documentation: Introduction
• Microsoft Learn: Virtualized domain controller architecture (VM-Generation ID)
• Microsoft Learn: [Detect and recover from a USN rollback](https://learn.microsoft.com/en-us/troubleshoot/windows-server/active-directory/detect-and-recover-from-usn-rollbac