How to detect and avoid tape shoe-shining?



I have DP 9.00 with HP StoreEver MSL 2024 G3 with one LTO-4 drive connected with SCSI to Windows 2008 R2 Server. Reading LTO4 spec, the tape should be fully written (or read) in about two hours but my backups take much longer. I don't know if there is a possibility to detect tape shoe-shining or if it is just guessing by backup speed. My test sessions:


Session 1
Disk Agent 1 took 217 minutes to write 570GB data, 44 MB / s (disk should do 60 MB/s)
Disk Agent 2 took 66 minutes to write 180GB data, 46 MB /s (disk should do 100 MB/s)
Total time 217 minutes, 750GB


Session 2
Disk Agent 1 too 140 minutes to write 700GB, at 70 MB/s (disk should do 200MB/s)


Session 3 (combines sources of Session 1 and Session 2)
Omnispeed shows 123 MB/s
..running just now, waiting for result


In all cases the disk agents and media agent are on the same machine, cell is on another machine, CPU is low.

Does it indicate shoe-shining? And solution is to run more disk agents (if possible) to feed enough data to LTO?


How does HW compression change the picture? Can I see statistics of the compression ratio? E.g. I can have 800GB of data on tape, but I don't know if the tape is full or just half filled. I could have data rate of 60MB/s but as they are highly compressible, the actual tape rate could be 20MB/s or lower.


I would be grateful for any information, I did spend some time googling but found nothing to answer my questions.


Kind regards, Jan