🔰 Overview
In Proxmox VE, when configuring a Backup Job, you can select one of three backup modes under the Mode option:
Snapshot, Suspend, or Stop
These modes determine how a virtual machine (VM) or container (LXC) is handled and locked during the backup process,
ensuring data consistency and reliable restore points.
🧱 1️⃣ Snapshot Mode (Default & Most Common ✅)
🔹 Principle
Uses QEMU Guest Agent, or storage-level snapshot technologies such as LVM, ZFS, or qcow2,
to create a live snapshot of the VM’s disk without shutting it down.
Backup data is read from the snapshot while the VM continues to run.
🔹 Advantages
- No noticeable service interruption.
- Supports online (hot) backup.
- Works with snapshot-capable storage (ZFS / Ceph / LVM-thin / qcow2).
- With QEMU Guest Agent, the guest OS can flush caches before backup for application-consistent snapshots.
🔹 Limitations
- May experience slight I/O performance degradation during backup under heavy load.
- If the underlying storage doesn’t support snapshots, Proxmox automatically falls back to Suspend mode.
🔹 Recommended Use Cases
| Scenario | Recommendation |
|---|---|
| Most VMs or LXCs | ✅ Strongly recommended |
| Systems requiring zero downtime | ✅ Recommended |
| Automated daily/hourly PBS backups | ✅ Ideal choice |
🧱 2️⃣ Suspend Mode (Pause Before Backup)
🔹 Principle
Temporarily pauses (freezes) the VM or container at the start of the backup.
Once the snapshot or dump is completed, the system resumes immediately.
This results in a short downtime backup.
🔹 Advantages
- Ensures file system consistency even on non-snapshot storage.
- Less impact than Stop mode — usually only a few seconds to tens of seconds of pause.
🔹 Limitations
- The VM or container is temporarily frozen (no I/O).
- Not suitable for high-availability (HA) environments, as the system may interpret it as a node failure.
🔹 Recommended Use Cases
| Scenario | Recommendation |
|---|---|
| Storage without snapshot capability | ✅ Recommended |
| Test databases or systems needing strong consistency | ✅ Suitable |
| Systems tolerant of brief interruptions | ⚙️ Acceptable |
🧱 3️⃣ Stop Mode (Full Shutdown Backup)
🔹 Principle
Performs a graceful shutdown of the VM or LXC before backup.
After the backup completes, the system restarts automatically.
This produces a cold backup with full data integrity.
🔹 Advantages
- Guarantees 100% data consistency (all buffers written to disk).
- Works on any storage type — no snapshot support required.
🔹 Limitations
- Causes longer service downtime (shutdown → backup → startup).
- Not suitable for 24/7 or production systems.
🔹 Recommended Use Cases
| Scenario | Recommendation |
|---|---|
| Storage without snapshot support (e.g., raw or passthrough disks) | ✅ |
| Test or non-critical VMs | ✅ |
| Scheduled maintenance backups (e.g., overnight) | ✅ |
🧭 4️⃣ Comparison Table
| Mode | Service Interruption | Consistency | Snapshot Required | Best For |
|---|---|---|---|---|
| Snapshot | ❌ None | High (with Guest Agent) | ✅ Yes | Most systems, production workloads |
| Suspend | ⚙️ Short pause | Very high | ❌ No | Environments tolerant of brief pauses |
| Stop | ⏹️ Long downtime | Perfect | ❌ No | Maintenance windows, testing, cold backups |
💡 Practical Recommendations
| System Type | Recommended Mode |
|---|---|
| General-purpose VMs (Windows / Linux) | Snapshot |
| Containers (LXC) | Snapshot (if supported) or Suspend |
| Storage without snapshot capability (e.g., local-lvm) | Suspend |
| Databases / ERP requiring strict consistency | Snapshot + Guest Agent or Suspend |
| Long-term archived or inactive VMs | Stop |
✅ In Summary
Snapshot Mode is the best choice for almost all production environments.
Use Suspend or Stop mode only when your storage or VM type does not support snapshots.
Snapshot = Modern, Fast, Safe.
Suspend = Reliable for Legacy Systems.
Stop = Simple but disruptive.