Backup of an agent fails. The core displays the following error message:
"Transfer of volume 'D:\' failed
System.AggregateException: One or more errors occurred. ---> System.AggregateException: One or more errors occurred. ---> System.AggregateException: One or more volume stream readers failed ---> Replay.Core.Contracts.Transfer.CoreVolumeTransferNetworkErrorException: Agent dropped the network connection during data transfer. Check the agent log for possible errors."
This error is indicative of problems on the agent server. Generally these problems are caused by failures of VSS to keep the shadow copy available. Check the agent system event log for possible errors. One possible error is:
Volsnap Error Event ID 25
"The shadow copies of volume D: were deleted because the shadow copy storage could not grow in time. Consider reducing the IO load on the system or choose a shadow copy storage volume that is not being shadow copied."
This error indicates that VSS is deleting the shadow copy that AppAssure is using to back up data on the volume. Hence, the backup fails because AppAssure can't find the data blocks it needs to complete successfully. In this case the AppAssure agent then stop s transferring data to the core server causing the error message stating the agent dropped the network connection.
When VSS creates a shadow copy it writes the data to the volume it is creating the shadow copy of. If the disk is fragmented then VSS doesn't have a contiguous storage location and must write the shadow copy across a large portion of the disk. As a result, VSS fails to grow the shadow copy storage within it's timeout window. The Volsnap Error is then logged indicating that there is high IO on the disk.
Run a disk defrag of the failing volumes on the agent. Defragmenting the disk provides a contiguous storage location for the shadow copy. This reduces the IO load and increases the speed at which VSS can perform the shadow copy.
Run a chkdsk of the failing volumes on the agent. Chkdsk will ensure there are no issues with the file structure of the disk that could cause delays in the creation of a shadow copy
Reduce the IO load that AppAssure creates by modifying the following transfer settings: