Dell AppAssure snapshots fail after a while.

Recently I noticed a problem with snapshots not completing for one particular protected machine.
It was strange because the snapshot would start ok but always seemed to fail after approximately 40-45 minutes or after approximately 80GB had transferred.

The error on the core was as follows;

System.AggregateException: One or more errors occurred. —> Replay.Core.Contracts.Transfer.CoreTransferFailedException: The transfer of one or more volume images from a protected machine to the Core has failed —> System.AggregateException: One or more errors occurred. —> Replay.Core.Contracts.Transfer.CoreVolumeTransferFailedException: The transfer failed for volume ‘C:\’ —> System.AggregateException: One or more errors occurred. —> Replay.Core.Contracts.Transfer.CoreVolumeTransferNetworkErrorException: The agent dropped the network connection during the data transfer. Check the agent log for possible errors.

To me it looked like a network issue, in fact the AppAssure core logs seem to suggest the socket was being dropped.

After a little bit of head scratching, it turned out this wasn’t the issue at all.

Looking at the AppAssure agent logs on the protected machine revealed;

Failed to open ‘\?\GLOBALROOT\Device\HarddiskVolumeShadowCopy1212’ – The system cannot find the file specified

So it looked like the VSS snapshot was disappearing.

Long story short this turned out to be an issue with the snapshot size exceeding the % of volume allocation for VSS snapshots.

To resolve is quite simple, just run the following cmd from an elevated cmd prompt and change the drive letter to suit the volume that is failing.

vssadmin  resize shadowstorage /for=<drive letter:> /on=<drive letter:> /maxsize=unbounded

This is detailed in a Dell KB on the subject which you can find at

After running this, AppAssure successfully completed a snapshot and I could count the additional grey hairs that had appeared along the way.

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