[Veritas-bu] bptm and BUFFER tuning

I have read with interest recent messages (and the Veritas web page at 
http://seer.support.veritas.com/docs/183702.htm) about tuning NET_BUFFER_SZ, 
SIZE_DATA_BUFFERS and NUMBER_DATA_BUFFERS for better performance...but now I 
realize I'm confused about which way I need to focus my attention.
   My environment is NBU 3.4 on Solaris (the Media Servers run 2.6, and the 
Master Server runs 8); each Media Server has a Sun L9 library, which holds a 
Quantum 8000 DLT and nine tapes.
   In my bptm logs, I find the following entries side-by-side:
---- begin log sample ----
21:51:46 [29568] <2> fill_buffer: [29567] socket is closed, waited 
   for empty buffer 3 times, delayed 3 times, read 4738656 Kbytes
21:51:46 [29567] <2> write_data: waited for full buffer 12820 times, 
   delayed 135496 times
22:25:26 [29971] <2> fill_buffer: [29970] socket is closed, waited 
   for empty buffer 19242 times, delayed 22981 times, read 9905792 
   Kbytes
22:25:26 [29970] <2> write_data: waited for full buffer 9057 times, 
   delayed 30164 times
----- end log sample -----
   Here's my questions:
   1. Have I changed things for the worse or the better by following Veritas' 
suggestions and making the following changes?
      NET_BUFFER_SZ = 64k
      SIZE_DATA_BUFFERS = 64 k
      NUMBER_DATA_BUFFERS is left empty, defaulting to 8
   2. Is it odd that some jobs wait for empty buffers, while other don't?
   3. What's the difference between the fill_buffer entries and the write_data 
entries? Do the write_data complaints about waiting for full buffers refer to 
the tape library going idle because NBU can't supply it with enough data? If 
so, then what do the fill_buffer complaints about waiting for empty buffers 
refer to?
   Thanks for any suggestions anyone can offer.
-wde
--
Will Enestvedt
UNIX System Administrator
Johnson & Wales University -- Providence, RI