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Failed to call RPC function 'Vss.FinishSnapshot'

KB ID: 2825
Product: Veeam Backup & Replication | 9.0 | 9.5 | 10 | 11 | 12 | 12.1 | 12.2
Published: 2018-12-13
Last Modified: 2024-07-29
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Article Applicability

The first part of the error document in this article, Failed to call RPC function, is common and occurs anytime an RPC function cannot be invoked.

This article is specifically related to an issue where the VSS snapshot closes prematurely because the KeepSnapshot RPC calls from the Veeam Backup Server were not received by the VeeamVssSupport service within the guest.

Please review the logs carefully to confirm the applicability of this article.

Challenge

A job utilizing Application-Aware Processing fails with either of the errors:

  • Failed to call RPC function 'Vss.FinishSnapshot': Error code: 0x800401fd. Failed to invoke func [FinishSnapshot]
    
  • Failed to call RPC function 'Vss.KeepSnapshot': Error code: 0x800401fd. Failed to invoke func [KeepSnapshot]
    

A correlating entry can be found in the VeeamVssSupport log on the machine that was being backed up:

2:25:06 PM    224  INFO                RPC: KeepSnapshotEx
2:25:06 PM    224  INFO                        Keep snapshot. JobId: {vss_job_guid}
2:25:06 PM    224  INFO                            Snapshot job id: {vss_job_guid}, ttl: 1200.
2:25:06 PM    224                                  KeepSnapshot. TTL: [1200]
2:25:06 PM    224  INFO                        Keep snapshot. JobId: {vss_job_guid}. Ok.
2:25:06 PM    224  INFO                RPC: KeepSnapshotEx. Ok.
2:45:07 PM   4484  WARN            Snapshot timeout occurred.

Addtional log examples are available in the More Information section.

Cause

This error occurs when the guest OS fails to receive a keep-alive request (KeepSnapshotEx) within the configured snapshot timeout window. This may occur due to issues within the machine itself or external factors (e.g., network connection dropout, guest OS I/O performance, virtual environment disk performance).

Solution

Understanding KeepSnapshotEx Calls

During Application-Aware Processing preparation, a temporary service (VeeamVssSupport) is deployed to manage VSS snapshot operations within the guest. This service is programmed to close the VSS snapshot if it does not receive keep-alive calls during a set timeout period. By default, the snapshot timeout window is 20 minutes. The Veeam Backup Server sends KeepSnapshotEx calls every X seconds (where X equals VSSGuestSnapshotTimeout divided by 4). This timeout window ensures that, should something occur external to the machine, the VSS snapshot will not remain active indefinitely.
 

Adjust Snapshot Timeout Timing

If this issue occurs persistently, the snapshot keep-alive timeout window can be changed by modifying the following registry value on the Veeam Backup Server.

Note: This will affect all machines that are processed using Application-Aware Processing.

Key Location: HKLM\SOFTWARE\Veeam\Veeam Backup and Replication\
Value Name: VSSGuestSnapshotTimeout
Value Type: DWORD (32-Bit) Value
Value Data(Default-Decimal): 1200 [seconds]

No reboot or service restart is required; the new timeout value will be used during the next job run.

 

More Information

The examples below demonstrate:

  • A network connection drop that was long enough to prevent the VeeamVssSupport service from receiving a KeepSnapshotEx call within the timeout window.
  • The VeeamVssSupport service closing the snapshot due to the snapshot timeout.
  • The network connection resuming, which allows the VeeamVssSupport service to receive the KeepSnapshotEx or FinishSnapshotEx call; however, it fails because the timeout had already been triggered, resulting in the closure of the snapshot.
vSphere VM Guest OS Snapshot Timeout Example
2:25:06 PM    224  INFO                RPC: KeepSnapshotEx
2:25:06 PM    224  INFO                        Keep snapshot. JobId: {vss_job_guid}
2:25:06 PM    224  INFO                            Snapshot job id: {vss_job_guid}, ttl: 1200.
2:25:06 PM    224                                  KeepSnapshot. TTL: [1200]
2:25:06 PM    224  INFO                        Keep snapshot. JobId: {vss_job_guid}. Ok.
2:25:06 PM    224  INFO                RPC: KeepSnapshotEx. Ok.
2:45:07 PM   4484  WARN            Snapshot timeout occurred.
2:45:07 PM   4484                      Notifying writers about the 'BACKUP FINISH' event.
2:45:07 PM   4484                          Truncate logs: [false].
2:45:09 PM   4484                              Collecting statuses of the writers.. Ok.
2:45:09 PM   4484                          Deleting exported registry file: [C:\Windows\system32\config\SYSTEM.{7120084AB0-E15A-44A4-8E9E-1B8D82698635}]
2:45:09 PM   4484                      Notifying writers about the 'BACKUP FINISH' event.. Ok.
2:45:09 PM   4484              Waiting for backup completion. Ok.
2:45:09 PM   4484  INFO        Terminating the snapshot set. Snapshot set ID: [{snapshot_id}].
2:45:09 PM   4484  INFO        Terminating the snapshot set. Snapshot set ID: [{snapshot_id}].. Ok.
2:46:46 PM   1052  INFO        RPC: KeepSnapshotEx
2:46:46 PM   1052  INFO                Keep snapshot. JobId: {vss_job_guid}
2:46:46 PM   1052  INFO                    Snapshot job id: {vss_job_guid}, ttl: 1200.
2:46:46 PM   1052  INFO                Keep snapshot. JobId: {vss_job_guid}. Failed.
2:46:46 PM   1052  ERR             Cannot process external KeepSnapshotEx command.
2:46:46 PM   1052  ERR                 Freeze job already stopped.
2:46:46 PM   1052  INFO        RPC: KeepSnapshotEx. Failed.
Hyper-V VM Guest OS Snapshot Timeout Example
2:01:17 PM   7372  INFO        RPC: KeepSnapshotEx
2:01:17 PM   7372  INFO                Keep snapshot. JobId: {vss_job_guid}
2:01:17 PM   7372  INFO                    Snapshot job id: {vss_job_guid}, ttl: 1200.
2:01:17 PM   7372  INFO                        KeepSnapshot. TTL: [1200]
2:01:17 PM   7372  INFO                Keep snapshot. JobId: {vss_job_guid}. Ok.
2:01:17 PM   7372  INFO        RPC: KeepSnapshotEx. Ok.
2:21:27 PM   8092          CompletePending...
2:21:27 PM   8092          Complete pending.
2:21:27 PM   8092          Executing command [4].
2:21:27 PM   8092          Waiting for remote thread
2:21:28 PM   8092          Getting thread exit code.
2:21:28 PM   8092          Thread exit code is 0
2:21:28 PM   8092          CompletePending result [0x0]
2:21:28 PM   8092          Total services: [224]
2:21:28 PM   8092          Service name: [vmicvss]. Process id: [2732]
2:21:28 PM   8092          Done
2:21:28 PM   8092          Restarting HVVSS service.
2:21:28 PM   8092          Cannot read retry settings from registry. Using default value 4. Cannot read VmicvssRetryNumber value
2:21:28 PM   8092          Win32 error:The system cannot find the file specified.
2:21:28 PM   8092           Code: 2
2:21:28 PM   8092              Restarting Hyper-V VSS requester
2:21:28 PM   8092                  Stopping Hyper-V VSS Requester
2:21:28 PM   8092                  Cannot read meta file size settings from registry. Using default value 60. Cannot read StopServiceTimeout value
2:21:28 PM   8092                  Win32 error:The system cannot find the file specified.
2:21:28 PM   8092                   Code: 2
2:21:28 PM   8092                  Starting Hyper-V VSS Requester
2:21:29 PM   8092              Restarting Hyper-V VSS requester. Ok.
2:21:29 PM   8092          Finishing  CHvVssJob::StaticKeepAliveThread
2:25:26 PM   6296  INFO        RPC: FinishSnapshotEx
2:25:26 PM   6296  INFO                Finishing snapshot: job id: {vss_job_guid}, logs truncation required: no.
2:25:26 PM   6296  INFO                Finishing snapshot: job id: {vss_job_guid}, logs truncation required: no.. Failed.
2:25:26 PM   6296  ERR             Cannot process external FinishSnapshotEx command.
2:25:26 PM   6296  ERR                 Freeze job already stopped.
2:25:26 PM   6296  INFO        RPC: FinishSnapshotEx. Failed.
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