Backup: Failed to mount VSS AutoRecovery snapshot, check your log file for details

[LZuk62]

Domino is 14.5.1 HF43
OS is Windows Server 2022 (21H2)

mg2dom01#default#SNAP#20260709130101.log

Snapshot backup always fails (was running fine with 12.0.2 FPx), here is what is logged on the console (backupvss is already started with "-d"):
BackupVSS: DominoVSSWriter::OnIdentify called
BackupVSS: DominoVSSWriter::OnPrepareBackup called
BackupVSS: DominoVSSWriter::OnPrepareSnapshot called
BackupVSS: BackupVss: Volume Count: [ 5 ]
BackupVSS: Volume Name: [ \?\Volume{2bd2fcd8-f0d6-498a-9d7d-dcc70ebfed3e}\ ] Drive name: [ L:\ ] not found in [ E:\DataDom01 ] path
BackupVSS: Volume Name: [ \?\Volume{50b9c23f-14f1-4c22-b6c5-c4f1bdfc41bc}\ ] Drive name: [ C:\ ] not found in [ E:\DataDom01 ] path
BackupVSS: Volume Name: [ \?\Volume{f393ef64-52dc-480f-8365-2ab4b224d7c1}\ ] Drive name: [ E:\ ] found in [ E:\DataDom01 ]
BackupVSS: Found snapshot device for data directory: [\?\Volume{f393ef64-52dc-480f-8365-2ab4b224d7c1}]
BackupVSS: DominoVSSWriter::OnFreeze called
09/07/2026 15:01:01 BackupVSS: Domino Agent VSS Freeze Event received
09/07/2026 15:01:01 BackupVSS: backup command line: Binary path: [C:\HCL\Domino\nbackup.EXE] Param: [-vss]
09/07/2026 15:01:01 Backup: Domino Database Backup
09/07/2026 15:01:01 Backup: Started
09/07/2026 15:01:01 Backup: BackupNode: [mg2dom01], BackupName: [default], Translog Mode: [LINEAR], Backup Mode: [SNAP]
09/07/2026 15:01:01 Backup: LastBackupTime: 03/06/2026 09:20:55
09/07/2026 15:01:01 Backup: Starting backup for 464 database(s) [SnapShotMode]
09/07/2026 15:01:16 Backup: Ready for VSS Snapshot
BackupVSS: Requested backup operation done
09/07/2026 15:01:17 BackupVSS: DominoVSSWriter::OnFreeze Domino in Freeze Mode after 14 seconds!
BackupVSS: DominoVSSWriter::OnThaw called
BackupVSS: DominoVSSWriter::OnPostSnapshot called
BackupVSS: OnPostSnapshot - Backup type: COPY, Backup level: FRONT_END
BackupVSS: Mounting snapshot [\?\Volume{f393ef64-52dc-480f-8365-2ab4b224d7c1}] for [\?\Volume{f393ef64-52dc-480f-8365-2ab4b224d7c1}]
BackupVSS: OnPostSnapshot - Context: 0xb
BackupVSS: OnPostSnapshot - ComponentCount: 1
BackupVSS: OnPostSnapshot - Component [DominoDatabases] does not provide AutoRecovery
BackupVSS: Writable VSS Snapshot not supported - Not performing auto recovery.
09/07/2026 15:01:18 BackupVSS: Sending unfreeze to Domino Backup
09/07/2026 15:01:19 Backup: VSS Post Snapshot status reached after 2 seconds!
09/07/2026 15:01:19 Backup: Capturing changes in 464 database(s) [SnapShotMode]
09/07/2026 15:01:19 Backup: Failed to mount VSS AutoRecovery snapshot, check your log file for details
..... (router events removed)
09/07/2026 15:03:11 Backup: Pruning backups on VSS snapshot mode
09/07/2026 15:03:11 Backup: Pruned Database Backups: 1
BackupVSS: Requested backup operation done
BackupVSS: DominoVSSWriter::OnIdentify called
09/07/2026 15:03:12 BackupVSS: DominoVSSWriter::OnPostSnapshot Post backup changes applied after 103 seconds.
09/07/2026 15:03:12 Backup:
09/07/2026 15:03:12 Backup: --- Backup Summary ---
09/07/2026 15:03:12 Backup: Previous Backup : 03/06/2026 09:20:55
09/07/2026 15:03:12 Backup: Start Time : 09/07/2026 15:01:01
09/07/2026 15:03:12 Backup: End Time : 09/07/2026 15:03:11
09/07/2026 15:03:12 Backup: Runtime : 00:02:10.531
09/07/2026 15:03:12 Backup:
09/07/2026 15:03:12 Backup: [General ERROR!] - Failed to mount VSS AutoRecovery snapshot, check your log file for details
09/07/2026 15:03:12 Backup:
09/07/2026 15:03:12 Backup: All : 464
09/07/2026 15:03:12 Backup: Processed : 0
09/07/2026 15:03:12 Backup: Excluded : 0
09/07/2026 15:03:12 Backup: Pending Compact : 0
09/07/2026 15:03:12 Backup: Compact Retries : 0
09/07/2026 15:03:12 Backup: Backup Errors : 464
09/07/2026 15:03:12 Backup: Not Modified : 0
09/07/2026 15:03:12 Backup: Delta Files : 0
09/07/2026 15:03:12 Backup: Delta applied : 0
09/07/2026 15:03:12 Backup:
09/07/2026 15:03:12 Backup: Total DB Size : 0,0 Bytes
09/07/2026 15:03:12 Backup: Total DeltaSize : 0,0 Bytes
09/07/2026 15:03:12 Backup: Data Rate : 0,0 MB/sec
09/07/2026 15:03:12 Backup: --- Backup Summary ---
09/07/2026 15:03:12 Backup:
09/07/2026 15:03:12 Backup: Finished
..... (router events removed)
BackupVSS: DominoVSSWriter::OnBackupComplete called
BackupVSS: Requested backup operation done
BackupVSS: DominoVSSWriter::OnBackupShutdown called
09/07/2026 15:03:13 BackupVSS: DominoVSSWriter::OnBackupComplete Updating backup completed time

Thanks in advance
Luca

[Daniel-Nashed]

Please provide more details and context.

1. Did this work before? What changed since then?
2. Does it always fail or just some times?
3. What backup integration do you use? Is this Veeam?
4. How much databases do you have and how much data? I only see 464 databases in scope for backup this isn't big
5. What I can see is that the post snapshot apply takes 103 seconds. This is quite high and I don't know how this can happen for this small number of databases. But this isn't your root cause.

Here is the error message that indicates the root cause from what I can see:

 Writable VSS Snapshot not supported - Not performing auto recovery.

This brings be back to the question, what the integration you are using.
Please answer all my questions to have proper context.

Thanks

[Daniel-Nashed]

I am removing the bug label until this is a confirmed bug. With this level of information this cannot be categorized as a bug.
From what I see this is a config issue or an unsupported configuration eventually.

[LZuk62]

I am removing the bug label until this is a confirmed bug. With this level of information this cannot be categorized as a bug. From what I see this is a config issue or an unsupported configuration eventually.

Fine with me, I'm a newcomer and was not sure which label was the best :)

[LZuk62]

Please provide more details and context.

1. Did this work before? What changed since then?

2. Does it always fail or just some times?

3. What backup integration do you use? Is this Veeam?

4. How much databases do you have and how much data? I only see 464 databases in scope for backup this isn't big

5. What I can see is that the post snapshot apply takes 103 seconds. This is quite high and I don't know how this can happen for this small number of databases. But this isn't your root cause.

Here is the error message that indicates the root cause from what I can see:

 Writable VSS Snapshot not supported - Not performing auto recovery.

This brings be back to the question, what the integration you are using. Please answer all my questions to have proper context.

Thanks

Hi Daniel
please find my answers here below:

1. It was working fine with 12.0.2 (I don't remember the FP level, maybe 6 or 7)
2. This stopped working the day we upgraded from 12.0.2 to 14.5.1 (yesterday I installed HF43 upon direction from the support, but nothing changed)
3. We're using Veeam 12.3.2.4465
4. there are 460 files between databases and templates (don't know why it says 464) and the total amount is a bit less than 420GB

Regards
Luca

[Daniel-Nashed]

It might not have worked in 12.0.x. But the problem was not detected. There was logic added to detect none auto recovery snapshots and fail the backup.

Before it continued and the backup was incomplete. Now you might see an error case due to misconfiguration.

Can you please provide details about what virtualization you use?
Currently with Veeam only vSphere supports auto recovery snapshots.

Please explain exactly what you are using. Some examples:

• VMware vSphere --> requires specify configuration in the Veeam job in the storage tab as listed in documentation
• Hyper-V -> does not support Auto Recovery snapshots at all
• Veeam backup agent installed on the Windows host --> Fully support Auto Recovery snapshots

The devil is in the detail. And that's not a Domino Backup only challenge. This is the nature of VSS in combination with the backup software and virtualization layers.

[LZuk62]

Hi Daniel.
Customer is telling me that they're using Azure Local (which seems to be an evolution of Hyper-V) So we're in the worst scenario.
Being an ignorant on Veeam and MS world, is there a way to have VSS backups without Auto Recovery so that we have a consistent backup?

Thanks in advance
Luca

[Daniel-Nashed]

With Hyper-V there is no way to get auto recovery working.
Without auto recovery snapshots there is no chance that we can merge in the delta files and they would need to be backeduped separately.
This is possible but a much more complex restore flow. you first need a place where you store the files.
You could leave them on the box and take a separate backup just in case and let Domino backup handle those files.
But you would always need Domino restore to restore the files to merge in the deltas.

There is another way with Veeam. You can use the Windows agent like some other customers do. But then it would be a different type of backup. But would work with a Veeam server.