How are you going to set up cold storage for all that? Not going to be cheap if you go tape.
You don't...the data is overwritten FIFO. The 30 or 45 days of storage is how long they can record, and store before, the FIFO occurs.
The back end, and rather boring story to this is modern camera use analytics. The don't gum up the network spitting out hours of useless shit. I can use on-board intelligence to record only on motion based events. So if a camera sits there for 24 hours and one 1 event happens for 5 min, all it sends to the NVR is a time stamped, 5 min clip instead of 23hrs, 55 min of shit, and 5 min of event.
This customer is an odd duck and wants 100% recording...so all cameras firing all day, every day, recording countless hours of nothing with things mixed in. That many cameras recording 24/7 is not only nearly 2Gbps of internal network consumption, but it will take a serious amount of HDD space to record all of that useless shit. So now I had to bid new backbone fiber and heavier switch-gear to handle this load...on top of the servers. It drove the bid price nearly $100K...
Just wait until the first time they need to find an event and they have to sift through hours of shit "old-school" style...I guarantee you he'll want motion based recording enabled after that bullshit...