The problem with this type of Configuration is the distribution of the Deduplicated Data (note - CommVault won't allow you to setup this way with GDDB, Per Storage Policy Copy only one GDDB can be associated).
If you are going to use Disk_LibB as an additional library to handle the Backup, if Disk_LibA is offline, what will happen is the deduplicated Data will be spread to the Disk_LibB. Now you will end up with two-point of failure, where even one Disk Library is offline (due to Deduplication), the restore might not work.
Adding to the fact that this is across two sites, your bottleneck is also the network bandwidth.
The workaround is to create another Disk Library using the same Backend Disk Storage as Disk_LibB, and add it to the Data Path. (Again this is not recommended).
Hopefully that helps