Snapshot returned error code -121 / Final error (-121 The semaphore timeout period has expired.)

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Problem

This article describes the causes and possible solutions for the following errors:

  • Snapshot returned error code -121
  • Final error (-121 The semaphore timeout period has expired.)

Cause

The error code -121 is an official Microsoft System Error Code for The semaphore timeout has expired. Generally, these issues relate to latency or lag in the responsiveness of the network that occurs when the ShadowSnap Agent Service transfers a backup job to the Datto device. These issues may be related to the following:

  • The agent is experiencing networking issues when trying to write the backup image to the Datto device.
  • The agent is experiencing a timeout when attempting to write data.
  • Something is preventing large data transmission across the network. Some Antivirus programs will lock access to files if data is being constantly manipulated.

Possible Solutions

To minimize transient errors, update the ShadowProtect and ShadowSnap agents to the latest version found at download.datto.com, and reboot the target machine.

Network Troubleshooting

This error can be caused by a network communications issue between the Datto appliance and the protected machine. Make sure that you have read the Datto Networking Requirements. To test and solve, try these steps:

  • Can the Datto be accessed from the machine? Test ping and UNC paths to the device.
  • Create a NAS share on the Datto device and try writing data to that share from the protected system.
  • Add exceptions to any Antivirus or Firewall software for the ShadowSnap application on ports 25566 and port 139, and the C:\Program Files (x86)\StorageCraft folder.
  • If protecting machines across multiple subnets, ensure that a static route is configured on the network or use an auxiliary NIC provided on the Datto SIRIS to communicate with this subnet.
  • Ensure that there is no firewall, proxy, or filter of any type is interrupting communication between the Datto SIRIS device and the ShadowSnap agent on TCP port 25566 of the protected system.
  • Try to replace the Ethernet Cable which is plugged in to the Datto SIRIS to help resolve any packet loss experienced as the result of a faulty Ethernet cable.

Server Health / Issues with the Protected Machine

Follow these steps to check for and correct problems on the target system:

  • Review the StorageCraft server tuning guide to improve the server reliability.
  • A minimum of 20% free space per protected volume, and 1 GB of RAM, need to be available on the production machine. If resources fall below these thresholds, backups will fail.
     

     Volume Utilization

    Status

    Comments

    0 – 70%

    Good

    Utilization is good.

    71 – 80%

    Warning

    Utilization is outside optimal limits. Monitor the volume growth and look at cleaning up unnecessary files and moving non-essential data to other storage.

    81 – 100%

    CRITICAL

    Volume is becoming critical. Snapshots will start to fail, disk queue lengths will increase. Create space.

    Figure 1: StorageCraft utilization best-practices.

  • Check for scheduled tasks that might conflict with the backup: Run schtasks on the Windows command line.
  • Review Microsoft Event Logs to determine if there are I/O issues present on any services and inspect the server's overall health. Compare the events around the time of the failed backup, and determine if there are conflicting services.
  • Look for VSS events. If you see VSS events 12293 or 12298, see the following article: http://www.storagecraft.com/support/kb/article/211
  • Look for VSNAPVSS events. If you see any, see the following article: http://www.storagecraft.com/support/kb/article/210
  • Restart the Microsoft Volume Shadow Copy service. If you see the error message "Windows could not stop the Volume Shadow Copy service on Local Computer. Error 1053: The service did not respond to the start or control request in a timely fashion," ensure that the server's Page File size appears to be adequate, and reboot the server to clear the hung service.

If all above steps fail, perform a chkdsk /r and a disk defragmentation on the target machine.

Contacting Technical Support

If you need to contact technical support, please be prepared by collecting the ShadowProtect Diagnostic logs.

Additional Resoures

Event ID 12289 — Volume Shadow Copy Service Operations
How to determine the appropriate page file size for 64-bit versions of Windows


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