I'd first check if this drive is ok - stop networker, mount an empty (!!!) 
volume manually and write to 
the device with dd from /dev/zero (hope you are using some UNIX).
If you are not reaching the full LTO speed with variable blocksizes you have to 
think over 
connection/drive-HW issues.

If you are reaching the full LTO speed with this test, you'll propably have the 
problem that your 
networker - or better your networker clients - can not give the minimal data 
rate the drive is needing 
so it's getting in start/stop mode with degraded performance. In this case you 
should think over 
your parallelism settings or maybe try staging...

   hth Stefan

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