Originally Posted by ThrashZone
No split the odds with a couple 4tb or 4-2tb
Never want all your cookies in one basket.
Actually, having "all your cookies in one basket" is not a problem as long as you have another backup. Assuming the OP will be backing up 8TB of data (either now or eventually), if he splits all his data between two 4TB backup drives and one backup drive becomes infected with malware, becomes corrupted, or just fails, he will lose half his data. While losing half of one's data is better than losing all of it, there is no reason to lose any of it.
A better choice would be to have two 8TB external backup drives, one kept onsite and the other one kept offsite. That way, if something happens to one backup drive, he will still have the other one to fall back on. If two 8TB backup drives is not in the budget right now, one 8TB backup drive will do for now until he can afford the second one.
The things to keep in mind include any drive is subject to failure at any time, no matter it's age or price, and that data loss isn't always caused by drive failure. Viruses and other malware (such as ransomware), fire, theft, flood, user error (such as accidental deletion), etc. can all cause data loss. The only way to protect against those is to have at least three separate
copies of your data, such as on the computer, on an onsite backup drive, and on an offsite backup drive.
I prefer using internal type drives in an external dock or a hot swap bay in the computer for backup drives because internal type drives usually are better quality than external type drives (manufactures usually assume that external drives will not run as much as internal drives and, thus, feel using a lower quality drive in an external drive is justifiable). Also, when you have multiple external backups, you will need only one dock with its own PSU (or no PSUs if you use an internally mounted hot swap bay) instead of multiple enclosures and PSUs.
Someone else will have to recommend which HDDs to buy since I switched over to using all SSDs a few years ago and a lot of changes have happened with HDDs since then.