nb catalog more than 5TB

Hi,

I have one master server with 7.5 running on redhat 5.8 including media server.

another 4 media servers with same 7.5 version with linux os and one windows os.

No of NB clients are 2000.( exchange, sql , vms, oracle, bmr ). Also have 4 NDMP Datadomain.

I have been told that we are having more than 4.5 TB of catalog (  I am new to env and waiting for the access to servers / got access to opscenter readonly )

Any suggestions / recommedations how do we migrate to newer version.

few of my peers says migrating catalog with 4.5 TB is highly impossible, we need to prune the catalog to migrate, Is that true ?

If Yes, the best methods to prune the catalog ?

How to migrate the the NB version to 7.7.

Awaiting for replies

Thanks