"The VSS Diff failed" error

Issue

The "VSS Diff failed (An error occurred during the fast difference check; a slower method will be used instead)" issue has occurred.

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Cause

This issue is usually caused by the shadow storage size being too small.

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Resolution

Windows workstations 7, 8, 10, 11:

1. Use the command line and run the following command to resize the shadow storage:

vssadmin resize shadowstorage /for=X: /on=X: /maxsize=320MB

1. X represents the disk letter (it is recommended to perform this operation on all accessible disks).

vssadmin resize shadowstorage /for=X: /on=X: /maxsize=30%

1. After making the changes, run the backup task again. If it still fails, contact our technical support by submitting a request.

Windows Server:

1. Delete all shadow copies using the following two additional command line commands:

diskshadow

delete shadows all

1. Run the backup again. If it still fails, contact our technical support by submitting a request.