Case # 03105453
Tape jobs were running at 40MB/s instead of the usual 100+MB/s
SMB signing was turned on.
I have disabled this and jobs have resumed their normal speeds.
This signing could be set in 2 places - Group Policy or the registry
Group Policy (preferred method)
Computer Configuration, Policies, Windows Settings,Local Policies, Security Options,Microsoft network client: Digitally sign communications (if server agrees)
It can be viewed in Powershell by running
Look out for
EnableSecuritySignature : True
RequireSecuritySignature : False
As long as RequireSecuritySignature is set to false (0) then it is turned off.