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- Failed to call RPC function 'Vss.FinishSnapshot'
Failed to call RPC function 'Vss.FinishSnapshot'
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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
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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