Boi that is great! Do you publish your data/experiences somwhere? And also did you throw some of the high/ultra endurance models in the mix (normally for video surveillance and stuff)? I had so many normal micro SDs fail for i dont trust them anymore and rather grab one of these…

I use several Toshiba MG07/08 in 14 TB. Datacenter drives, CMR, Helium filled, not noisy, 5 year warranty, fast, often relatively cheap.

Buy a brandname M.2 SSD in low capacity variant and put it in an external case. A bit bigger then a thumbstick, but not as big as an 2,5hdd. If the casing fails (breaking of the usb port for example) you can switch the drive to another case or put it internal in a pc.

A bit more pricey solution, but usb thumbdrives get mostly the lowest quality flash chips.

so an icy box IB-1817M-C31 case is around 30€, add an 128 or 256 gb m2 nvme SSD for around 20€.

It depends much on your handling. If you transport the drive often, i would recommend an SSD, because they are not influenced by vibration, drops etc like an HDD is and will survive a lot of trips in hot and cold. All my dead drives were external HDDs that were transported around.

If you dont transport it, i would go for an HDD, because it is unbeatable in price per Terrabyte in comparison to an SSD. If you have a reliable 3-2-1 Backup strategy, it will be replaced if it fails, but none of your data is in danger.

As you said, you want to not needing to be connected to power, this rules out 3,5HDDs and limits you to 2,5HDDs or SSDs. There you pay double for an 4Tb SSD vs 4TB HDD.

SSDs tend to corrupt Data much faster than HDDs if unpowered for a long time (if archival is more your intention). Lifespan of an SSD is in the TBW, so the more data you write, the sooner it fails. A 4TB Samsung 870 QVO fails after 2880 TBW. A HDD writes ands stores data as long as it mechanically works.

A HDD stores Data upowered for a longer time and could last Years if handled correctly (i phased out a 2007 drive this year, run daily and still working without problems, just too small).

i would say, id depends very much on your usecase.

If you plan to do more of archival saving, rethink your power limitation. 2,5HDDs have right now hit kind of a wall in maximum capacity. if you go 3,5HDDs they are unbeataable in price to size. You get there nearly double the capacity per money spent vs 2,5HDDs, exspecially with bigger drives like 12, 14 or 16TB.