Storing snapshots,

When I saw the snapshot, I had questions that I was puzzled.

Snapshots need the support of resource LUNs. If the capacity of the resource LUNs is insufficient, the snapshot technology cannot be used. So in the actual work process, how large is the size of the resource LUN generally set?

1. If the customer's storage uses snapshots as a backup system, and snapshots are taken every night, what is the appropriate size of the resource LUN?

2. Whether the snapshot of the resource LUN is overwritten, for example, when the size of the resource LUN is not enough, the content of the first snapshot will be overwritten when the snapshot is taken, and so on...?

3. Resource LUNs are divided into A and B controls. So in actual use, do you also need to make snapshots for both A and B controls to make snapshots for customer storage?

Thanks