What can be causing a lot of network traffic between 2 media servers over port 1556?

[LT2013]

Hello.

I was recently informed that network traffic between 2 media servers was taking up a lot of bandwidth between 2 Data Centers. Here is the setup:

2 sites: Prod and DR. Master and a media server in Prod; media server writes to a Data Domain (via boost/OST). In DR, I have a media server, also backing up to a local DD, as well as a tape library. All servers are RH linux, running NBU 7.5.0.6.

Pretty standard config, using SLPs to duplicate as follows (the "-->" indicates and indent):

PROD-SLP

Backup to PROD-DD

--> Duplication to DR-DD

--> --> Duplication to Tape

DR-SLP

Backup to DR-DD

--> Duplication to PROD-DD

--> Duplication to Tape

So I should be writing to tape from the DR backup on the DD. I also have "Use only the following media servers" checked off in the Storage Unit setup for the DD disk pool.

The traffic can't be the DD-to-DD duplication, as those go over a different port. What I've noticed in the duplication to tape jobs, is that NBU will assign either media server to the DR-DD to read from. So in essence, the cause of all this network traffic could be the PROD media server reading and hydrating the data from the DR DD, then sending it to the DR media server for tape out. Any way to restrict this to only read from DR DD from the DR media server?

[LT2013]

I think I may have found my answer in: https://www-secure.symantec.com/connect/forums/netbackup-doesnt-use-correct-mediaserver-duplication

[mph999 · Accepted solution]

Common server for dup option may help :

nbemmcmd -changesetting -common_server_for_dup <default|preferred|required> -machinename master server name

Select from the following options:
■ default
The default option (default) instructs NetBackup to try to match the
destination media server with the source media server. Using the default
option, NetBackup does not perform an exhaustive search for the source image.
If the media server is busy or unavailable, NetBackup uses a different media
server.
■ preferred
The preferred option instructs NetBackup to search all matching media server
selections for the source. The difference between the preferred setting and
the default setting is most evident when the source can be read from multiple
media servers, as with Shared Disk. Each media server is examined for the
source destination. And for each media server, NetBackup attempts to find
available storage units for the destination on the same media server.
If all of the storage units that match the media server are busy, NetBackup
attempts to select storage units on a different media server.
Network Optimized Backups
Network Optimized Duplication
122
■ required
The required option instructs NetBackup to search all media server selections
for the matching source. Similar to the preferred setting, NetBackup never
selects a non-common media server if there is a chance of obtaining a common
media server. For example, if the storage units on a common media server are
busy, NetBackup waits if the required setting is indicated.
Rather than fail, NetBackup allocates source and destination on different
media servers.