Thanks for testing and provided the logs.
The first job it takes about 3 hours, the second job take about two and half hours , the difference between these two jobs are half hours.
The bottleneck is showing below
First job: Load: Source 8% > Proxy 13% > Network 11% > Target 99%
Second job: Load: Source 13% > Proxy 21% > Network 14% > Target 98%
Both bottlenecks are target, which is your process rate will depend on the target, 1% writting speed difference is acceptable.
You can also see where the proxy and network are on different load each time, where you have same backup size.
I know the difference between 2.5 and 3hrs is 'half hour'.. and i also know that the difference between 98% and 99% is 1%. I also know from the processing stats that its showing the Tape to be the bottleneck.
I did not lodge a support case and upload all the logs to only be told the obvious !?
What i want to know is why is there extended periods of absolute no activity ? Why is the data processing rate so low when everything is connected to Fibre and that Tape Drive is capable of handling speeds upto 160MB/s with close to 20 brand new LTO6 tapes. And why am i sometimes able to complete the job in 1.5 hours and sometimes it takes more than 3 hrs !?