What to do: Datto SIRIS Snapshot Returned Error Code 121

by Sep 13, 2012Business Continuity

So you know what to do when you have a Datto SIRIS Snapshot Returned Error Code 121?

Like everything in this world, technology issues arise.  Knowing how to deal with issues when they do occur with your Datto SIRIS is crucial to the success of your backups and data recovery. Now, when you get a Datto SIRIS Snapshot Returned Error Code 121, you’ll know what to do!  Below are some troubleshooting solutions.

Backups fail with either error messages:

Datto SIRIS Snapshot Returned Error Code -121
stcx.SnapshotError (rc=500, err=1): Snapshot returned error code – 121 for VSNAP Direct; None.


The error code -121 is an official Microsoft System Error Code for “The semaphore timeout has expired.”  Semaphore Timeout Errors are caused by a very wide scope of specific issues.  Generally these issues relate to latency, or lag in the responsiveness of the network that occurs when the ShadowSnap™ Agent Service is transferring a backup job to the Datto SIRIS™ or SIRIS Lite™ Device.

1.   The agent is experiencing networking issues when trying to write the backup image to the datto device.

2.   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.


1. To minimize any number of transient errors that may appear, update the ShadowProtect and ShadowSnap agents to the latest version found at www.shadowsnap.com and perform a reboot of the target machine.

2.   Basic network troubleshooting:

• Check networking settings
• Can the datto be accessed from the machine
• Are the shares browsable
• Can shares be written to?
• Replacing the Ethernet Cable which is plugged in to the Datto SIRIS™ or SIRIS Lite™ may help resolve any packet loss experienced as the result of a faulty Ethernet Cable.
• Ensure that there is no firewall, proxy, or filter of any type that is interrupting communication between the Datto SIRIS™ or SIRIS Lite™ Device. and the ShadowSnap™ Agent on TCP port 25566.

• If protecting machines across multiple subnets please ensure that a static route is configured on the network or use an auxiliary NIC provided on the Datto SIRIS™ or SIRIS Lite to communicate with this subnet.

3.  Review the StorageCraft server tuning guide to attempt to improve the server reliability.


4.  Add exceptions to any Antivirus or FireWall for the ShadowSnap application on ports 25566 and port 139, and the C:Program FilesStorageCraft folder within the anti-virus program present on the server.

5. If all above steps fail, perform a chkdsk /r and a disk defragmentation on the target machine. Ensure that there is at least 10% of available free space on the operating system drive.

Hope this article was helpful in figuring out what to do with the Datto SIRIS Snapshot Returned Error Code 121. If not, contact us today!

Dale Shulmistra is a Business Continuity Specialist at Invenio IT, responsible for shaping the company’s technology initiatives -- selecting, designing, implementing & supporting business continuity solutions to bolster client operational efficiencies and eliminate downtime.