Netbackup 7.5.0.5 on Windows 2008 r2 - slow performance from DSSU to tape

Hello,

I have a new Windows 2008 r2 server running Master&Media server v7.5.0.5.

I have a Arcvault 12 tape library - which Windows 2008 r2 sees correctly in Device Manager and I have installed the latest HP drivers (v3.7.0.0) for the Ultrium LTO 4 that is in that library.

Backing up clients to a DSSU (basic disk).  That appears to work really well.

I can backup the DSSU to tape and everything works, except the tape drive backup speed is rock bottom - around 2MB/sec.

Running HP's tape tool on the system to test outside of NB, I get tape write speeds around 70MB/sec.

I've tried different SIZE_DATA_THIS and NUMBER_DATA_THAT settings with no tape write speed changes.

Any thoughts?

Thanks,

-Bill