Depends on what you're going to do with it.  I don't know the HP-UX platforms, 
but generally, the UNIX stuff is faster than the NT stuff, hardware wise.  Do 
you already have HP platforms and therefore HP smart folks?  Do you already 
have NT platforms and NT smart folks?  Are you going to backup more NT stuff 
than UNIX stuff?  I think the answers to these questions helps to lean you in a 
particular direction.

We've done quite a bit of performance testing with ADSM on NT.  I'm finally 
getting comfortable with the performance I'm seeing.  At first I was skeptical, 
but my confusion about how NT does things contributed to my confusion.  We've 
tested dual processor P6 configurations with 128 MB of memory and were unable 
to swamp the server with the clients we had.  We had two OpenVMS VAX 6610 
systems and a couple of Digital Alpha UNIX systems as clients.  We ran a number 
of concurrent streams into the server.  Looks like the limiting factor in this 
case was the driver on the VAXen rather than the server.  Migration from disk 
pools to tape is acceptable.  I've seen performance in the 2 - 2.5 GB per hour 
on a normal SCSI bus (10 MB/sec).

Boils down, IMHO, to what platform you are most comfortable with.  ADSM is 
identical in either case.

I would be interested in hearing about your final decision.  Can you please 
post it here along with the criteria you finally used?

Thanks,

Kelly Lipp