Gene,

>I'm backing up 4 MS Exchange servers--at the same time and approximately
17
>GB each--and getting a throughput of 1400 KB/sec (4.8 GB/Hr) on >average.
I
>add tree more MS Exchange servers to the backup and the rate drops by a
half
>to 670 KB/sec (2.3 GB/Hr).

You didn't mention what kind of network you have between the Exchange
servers and the ADSM server?  Also,are you going through routers or
switches?  From the info you did provide, I can make the following
observations:

With 4 concurrent sessions, you are getting an aggregate throughput of 5600
KB/sec (4 x 1400);  with 7 concurrent sessions, you are getting 4690 KB/sec
(7 x 670) .  This is a bit of a slowdown in aggregate throughput but not
that much.  What is the expected max throughput for your network
configuration (consider the type of lan, the NICs, any routers or switches
that may be in the path, etc.).  Another thing to look at is the ADSM
server configuration.  I presume that you are writing to a disk pool when
you backup.  What type of disks do you have and what is the rated write
speed of those?  You may get faster throughput writing directly to tape if
you have a fast tape drive...but then you would limit the number of
concurrent sessions to the number of tape drives you can make available for
the backup.

I guess the net of this is that there are many variables to be considered
but if you are sharing the same network resources, you should not be
surprised that the throughput for each individual exchange server will drop
when you add additional concurrent sessions... especially if you are
already at or near the physical bandwidth of your network.

Chris Zaremba
ADSM Agent Development
internet  zaremba AT us.ibm DOT com