The Tool Desk
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What the MARS agent backs up—and where it fits
MARS backs up files, folders, and system state from on-premises Windows machines to an Azure Recovery Services vault. It can also protect files and folders on an Azure virtual machine alongside the Azure VM backup extension. In a larger backup architecture, it can run on Microsoft Azure Backup Server (MABS) or System Center Data Protection Manager (DPM) servers. It is not, by itself, the usual method for protecting an entire Azure VM. See Microsoft’s guide to backing up Windows machines with the MARS agent for the supported scenarios.
| Deployment | What MARS protects | Context |
|---|---|---|
| On-premises Windows machine | Files, folders, and system state | Backs up directly to an Azure Recovery Services vault. |
| Azure virtual machine | Selected files and folders | Runs alongside the Azure VM backup extension when file- or folder-level protection is needed. |
| MABS or DPM server | Data in a secondary backup architecture | MARS is part of the server-based backup arrangement. |
Tip 1: Check prerequisites and connectivity before registration
Confirm that the machine and network are ready before installing or registering the agent. Microsoft recommends using the latest MARS agent version; an outdated agent can contribute to registration errors. The person installing and configuring it needs local administrator privileges, and the protected machine needs internet access.
- Verify network access: allow HTTPS traffic on port 443 to Microsoft Entra ID, Azure Storage, and Azure Backup endpoints. Use Microsoft’s MARS installation guide and its current endpoint guidance to configure allowlists. Avoid relying on a static IP list, which can change.
- Confirm TLS 1.2: make sure TLS 1.2 is enabled on the machine.
- Check system basics: install current operating-system updates and verify the system’s time-zone configuration.
Microsoft’s troubleshooting guidance states: “Ensure that the clock on the protected system is configured to the correct time zone.” An incorrect time-zone setting can complicate troubleshooting even when other setup checks appear correct.
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Tip 2: Protect the passphrase and prepare the cache
During registration, set the encryption passphrase and store it somewhere secure that is separate from the protected machine. Microsoft says it cannot recover backup data if the passphrase is lost. Microsoft recommends keeping it in a secure alternate location, such as Azure Key Vault.
Also choose a cache (scratch) folder that exists, is accessible to the agent, and has enough free space. Microsoft’s installation guide recommends free space of at least 5% of the data being backed up. Its troubleshooting guidance separately recommends keeping 5% to 10% of the volume free at the scratch-folder location. These are operational space recommendations, not performance guarantees; follow the applicable guidance for your configuration.
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If a cache-related operation fails, check that the folder still exists, is accessible, and has supported attributes. Confirm free space and adequate shadow-copy storage, and check whether antivirus software or another process is blocking access.
Tip 3: Confirm file support and investigate warnings
A successful or completed backup job does not necessarily mean every file was protected. A job can finish with warnings when one or more files are skipped. Review the MARS agent log and compare the affected data with Microsoft’s support matrix for the MARS agent before assuming a warning is harmless.
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- Reparse points and hard links
- Compressed streams and sparse streams
- Encrypted-and-sparse files
- OneDrive synced files, which use sparse streams
- Folders with DFS Replication enabled
Encrypted files are supported only when the MARS agent can access the necessary certificates. Because support details can change, consult the live support matrix for the specific file attributes and workload you intend to protect.
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Troubleshoot a failed backup or warning in order
Use this sequence to narrow down common causes. Microsoft’s Azure Backup agent troubleshooting guide provides additional checks and remedies.
Quick Recap
- Update the agent: check that the installed MARS agent is current.
- Check connectivity: verify internet access and HTTPS connectivity to the required Microsoft Entra ID, Azure Storage, and Azure Backup endpoints.
- Check the service: confirm that the MARS service is running.
- Inspect the scratch location: confirm that the folder exists, is reachable, has sufficient free space, and has supported attributes; check shadow-copy storage as well.
- Review the operating system and clock: install current OS updates and confirm the correct time zone.
- Check for interference: determine whether antivirus software or another process is holding file handles or otherwise blocking access.
- For warnings, inspect the log and support matrix: identify which files were skipped and whether an unsupported attribute or data type explains the warning.
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