About two weeks ago, I upgraded my NetWorker server from 7.6.1 to NetWorker 
7.6.3.4.Build.879. This server backs up 336 clients (mostly Windows and Linux). 
All of the clients back up to a Data Domain system using Boost and a few are 
cloned nightly to LTO-5 tape. I have 11 Boost devices configured for direct use 
on the server and each Boost device has its max sessions set to a value of 10. 
No storage nodes are involved in this data zone.

After we upgraded our DD system to the latest OS, the backups of larger servers 
improved in their throughput, but for the past few days, I am noticing an 
unusual number of backup failures for several groups of, both Linux and 
Windows, including some that also have NetWorker 7.6.3 on them. The error is 
always the same in the savegroup report "connection dropped."

There does not appear to be anything problems going on with network 
connectivity and in most cases, these clients do not back up via a firewall. I 
do not see any errors on the clients or the NetWorker server when I use 
"netstat -i." Incremental backups of the same clients also work without issue. 

I reviewed the NetWorker tuning guide on PowerLink, but I haven't done any of 
the tests they recommended yet with uasm, although it did contain a 
recommendation to increase client parallelism to 12, which I changed a few 
minutes ago. Most of the clients had the default setting of 4 for their 
parallelism.

If anyone has any ideas on how to investigate this problem, please let me know. 
I am skeptical that doing tests with uasm will bring forth any enlightenment on 
this issue.