There is no HDD that is 100% perfect and will last forever. the M-DISC is supposed to last over 100 years but it's capacity is only 100GB and the discs cost $30. each I have 4 discs for what is personal and is most important to preserve.

 

Seagate Expansion STKM5000400 5TB!?!

 

Someone already said it, but sadly large and cheap SSDs (usually SATA3) are the next big victim of the AI inflation after RAM.
Bye bye Samsung, it was good while it lasted...

Talking about HDDs, I usually go for 2TB. Partly because of the mentioned disaster when a huge drive breaks, although it's totally fine having them as long as you double backups. And partly because I'm staying away from UEFI as long as I can. No UEFI means MBR with 2GB max capacity.

 

Have you considered getting a RAID 0 (or better yet, RAID 5) configured array?

 

That's a good solution, but requires several disks, typically a NAS box. And all the drives in the RAID set are running at the same time.
Never in RAID0 though, that's for speed and even less reliable. RAID 1, 5 and 6 are the ones to go for backup.

 

Since we moved on to 'what 3,5" drive is best':
For long time storage I try to avoid helium filled drives. Not that I had any negative experiences with those. I have plenty of 18-24gb drives and none of them had issues. It's just, I guess the helium could disappear over time and that could potentially make the drive fail. So for the most important stuff I stick to 6gh and 8gb drives without helium filling.
(And pairs of course and a pair of different manufacturers of course)

(Edit: and it's best to have the drive running every now and then because of the lubricant in the bearings)