I can't say I've any experience of your configurations, but there are many 
things to check.

1.      Run NCVU on the Linux SAN Media server.  If you need to know how 
to, look on the Veritas web site.  It will highlight anything odd there. I 
think you can set up to run it on just the media seever - it is really 
designed for a Unix environment.

2.      We can discount the disk performance as you had it going Ok over 
the network.  Usually this is a good thing to look at. 

3.      Make sure you have the SIZE_DATA_BUFFERS set to something like 
256kb (262144).  If you don't you will get poor performance.   Set 
NUMBER_DATA_BUFFERS to 32 or more.

4.      Turn on logging to level 1, create the bpbkar and bptm folders 
under /usr/openv/netbackup/logs.   Look for the messages about how many 
times bpbkar and bptm waited (not certain you get them on Linux).  If you 
do they tell you for sure if you are waiting for the tape or the client.

5.      Test with synthetic data so you know just how compressible it is.  
HP have on their web site (hunt down their LTO tapes) some utilities for 
several o/s that create data files with known compressibility, test tape 
performance etc.  Some may work for you.

6.      Watch the drive, does it receive data continuously, or stop and 
have to back up.  If you are using a fabric, you can watch the data go 
through the switch (on brocade, portperfshow).     You can capture this in 
a terminal emulator, cut it about and run it through Excel to graph it.

You say the absolute fastest you see is 15MB/s - well funnily enough, the 
LTO1 drive native maximum data rate is 15MB/s.  So you are not doing 
badly, unless you were using compressible data.  The HP LTO drive is 
supposed to slow down to match the data rate - provided you have the right 
firmware, so check that out too.

William D L Brown