Avamar: On‑Disk Log File Gap Detected in Exchange Database Causes VSS Backup Failure

Summary: Avamar Exchange Volume Shadow Copy Service (VSS) backup fails with warning ‘On‑disk log file gap detected…’ and error 13077. Cause: missing logs from deletion, backup product, or circle logging. Fix: stop backup software, keep logs, disable circle log ...

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Symptoms

Exchange VSS Backup Failure Observed with Avamar

The following symptoms are reported when Avamar attempts to back up Microsoft Exchange using VSS:

  • Backup operation aborts with a warning indicating an on‑disk log file gap.
  • Backup process terminates with error 13077 indicating it cannot complete.

Full Backup Symptom Details

avexvss Warning <0000>: On-disk log file gap detected in database DBName between log indexes 0003EF1B and 00040AE1, terminating backup.
avexvss Error <13077>: Unable to complete backup.

Incremental Backup Symptom Details

avexvss Error <0000>: Log file gap detected in DBName5 between current backup and last backup.
avexvss Error <0000>: Highest log index from previous backup: 00103A84, lowest current log index: 001054BB, terminating backup.
avexvss Error <13077>: Unable to complete backup.
       

      Cause

      Log File Gap Leading to Exchange VSS Backup Failure

      Exchange generates transaction logs sequentially. During an Avamar backup, Avamar does not truncate the database logs; instead it signals the VSS framework, which instructs the Exchange Writer to request log truncation from Exchange. When the sequence of logs is broken, Avamar detects a gap and aborts the backup.

      Primary Causes of the Log Gap

      • Manual deletion of log files from the Exchange logs directory creates a discontinuity in the log sequence.
      • Use of additional backup software that truncates Exchange logs independently of Avamar, breaking the expected log order.
      • Temporary activation of circular logging on the Exchange database before an incremental backup, which forces log truncation and results in missing log indexes.

      Underlying Mechanism

      Because Avamar relies on the VSS framework to request log truncation, any external action that removes or truncates logs without updating the VSS state leaves a gap. Avamar then interprets the missing log indexes as a corruption condition and aborts the backup operation.

       

      Resolution

      Resolve “On‑disk log file gap detected” errors for Exchange VSS backups

      Checklist

      • Confirm you have administrative rights on the Exchange server and on the Avamar client.
      • Verify that the latest Avamar client is installed.
      • Ensure no other backup product is scheduled to run against the same Exchange databases.

      Remediation

      1. Disable any competing backup software.
        • Stop or uninstall third‑party backup agents that may also access the Exchange databases.
      2. Check for manual log deletions.
        • If you notice missing sequential log numbers, a gap exists.
      3. Repair the log gap.
        • Use the most recent backup copy of the missing logs or, if unavailable, run eseutil /r to replay transaction logs from the last full backup.
      4. Ensure circular logging is disabled.
        • Circular logging truncates logs without VSS coordination and creates gaps for incremental backups.
      5. Force a log truncation through VSS.
        • Run a full backup with Avamar to let the VSS writer request proper log truncation.  
       

      Additional Information

      Checking for Discontinuous Exchange Transaction Logs

      Discontinuous transaction logs can be identified using manual inspection or by using the built‑in Microsoft Exchange utility **Eseutil**.  
      Use caution when running **Eseutil**, as incorrect usage may result in database corruption.

      Manual Log Verification

      1. Log in to the Exchange server.
      2. Navigate to the transaction log folder for the affected mailbox database.
      3. Review the log file sequence and modification dates.
        Example:  
        Log Name       Modified Date
E0200040F75    2/11/2013 2:23 PM
E0200040F74    2/11/2013 2:23 PM
E0200040F73    2/11/2013 2:23 PM
E0200040AE1    2/8/2013 4:15 PM
        Interpretation:
        • Logs E0200040F73, E0200040F74, and E0200040F75 are sequential.
        • A log gap exists between E0200040AE1 and E0200040F73, which can cause backup failures.

      Checking Logs Using Eseutil

      1. Open an elevated Command Prompt window.
      2. Navigate to the transaction log directory for the affected database.
      3. Run the following command:  
        eseutil /ml <log_prefix>
        Example:  
        eseutil /ml E00
        Expected Output When Logs Are Missing If the log sequence has gaps, Eseutil reports the missing generation:   
        Missing log file: c:\program files\exchsrvr\mdbdata\E0002BE2.log
ERROR: Missing log file(s). Log file is generation 11,235 (0x2BE3), but expected generation is 11,234 (0x2BE2).
        In this example, the missing log file is: 
        E0002BE2.log

      Next Steps

      If either manual inspection or Eseutil identifies missing or discontinuous logs, contact the Exchange Administrator to determine the cause of the log gap and take corrective action.

       

      Affected Products

      Avamar

      Products

      Avamar, Avamar Plug-in for Exchange 2007, Avamar Plug-in for Exchange VSS
      Article Properties
      Article Number: 000036864
      Article Type: Solution
      Last Modified: 16 Mar 2026
      Version:  4
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