Well, then you have yourself the answer 😉
I have never worked with this device, but I already have worked on other devices that offered deduplication features.
But, on some, deduplication is performed seamlessly on the fly (achieving less dedup ratio but faster data access) as with PureStorage Flashblades for example, while for other it’s almost on the fly but with post-operation compression (like daily, or weekly...) as on Dell/EMC Datadomain for another example. Their purpose is to achieve better post-comp/operation deduplication ratios.
On the first case, it’s no problem but you may use more storage space, while on the second, it would “cost” you performance, especially while reading data out of this storage.
There are also devices where you can disable the deduplication.
If you let Commvault deduplication active on primary storage, and do not activate the Commvault deduplication on the new storage library, then data will be hydrated for your copy, and this is probably the scenario that would generate the more trafic between the two.