Assuming you need to “get up and go”, like a refugee situation, what are the chances that you’ll find a drive that can read Blu-ray disks, versus the chances that you’ll find a LTO tape drive ?

I have a normal PC...

I'd love some kind of external tape drive that I can connect with USB-C, or USB-3...

But everything is SAS? And no way to convert SAS to SATA?

Recommendations?

For this purpose, I think it would be nice to access the raw data, to see any errors that would be otherwise masked. As someone in the comments suggested, one might compare number of corrected errors in 1, 2, 5 years and compare to the number of redundant bits stored to estimate the expected longevity of the medium

Using HDDs for backup is also a terrible long term strategy, because you must have a lot of money regularly, to buy new HDDs to replace your old HDDs and this much more often than you need to buy a tape drive to migrate your tapes.

I have stored a lot of data on HDDs, and the only reason why I have not lost any of it yet is because I have always used duplicate HDDs. After 5 years or more, most HDDs had some corrupted sectors, but they were not in the same positions in the duplicate HDDs, allowing complete recovery of the data.

The reality is that both tapes and HDDs suck. What is really needed for long-term storage is a write-once memory with a lifetime of 100 years or more, based on an open standard that would ensure the availability of readers in the future.

If such a memory would use optical reading, it would have to use a great number of layers, filling a 3D volume, in order to achieve densities comparable with the magnetic media. While several research projects in this direction have been announced from time to time, until now none of them has resulted in a commercial product.

I bought a thunderbolt to FC adapter; works perfectly on Mac and Linux.

I mention LTO 4 because you can today, buy multi decades old LTO-4. Brand new. So in multiple decades from now, I assume you’ll be able to find LTO-7 or 8; brand new. A drive might cost a little more to obtain, but given the plethora of used multi decades old lto currently out there, it seems reasonable to expect that in a recovery scenario you’ll be able to shell out for the right drive.

But yes for most HDDs or the cloud are better. No need to get spicy about it.

You don't necessarily need a lib, though. Especially if you're interested in a use case where you can store data in a go bag, safe deposit box, etc., it seems like having individual tapes would be preferable.

Individual used drives aren't too expensive (or at least didn't used to be). Libraries, in contrast, do tend to be more expensive (and also a lot more trouble to ship).

That is easy for optical drives, because there is no direct relationship between the size of bits on the optical track and the dimensions of the read/write laser head.

For magnetic media, the gaps in the magnetic circuit of the read/write heads are optimized for a certain dimension of the bits from the tape material and the efficiency of the read/write process greatly diminishes for other bit sizes.

So there is no obsolescence policy, but there is a real technical difficulty in ensuring compatibility with older magnetic media with different bit densities.

Any guarantee made by manufacturer about data on tape longevity is irrelevant unless it is easy for user to create the storage conditions under which is warranted, and that is usually not cheap.

not hard to find stories about data on LTO tapes being unreadable after 5 years. The same as stories of data on even the worst CD-Rs being still readable after 30 years ( i can personaly attest to that).

The connection to a computer does not have any special challenges, except that the computer must be a desktop with a free PCIe slot.

Unless you have a server motherboard with an on-board SAS controller, you need to buy a SAS HBA card, put it in your desktop and also buy a compatible SAS cable, in order to connect an LTO tape drive to the computer.

New tape drives are extremely expensive, e.g. $4500 for the last generation of LTO-9 tapes (18 TB/cartridge), but if you store at least a few hundred TB of data you recover the cost of the drive from the cost difference between HDDs and tape cartridges.

I have an older LTO-7 (6 TB/cartridge) tabletop drive, which has cost me $3000 about 7 or 8 years ago (new), and there are several years since I have recovered its cost.

If you do not intend to store more than 100 TB, the cheapest solution is to buy external HDDs, but for long term storage you must plan to migrate the data periodically, as the lifetime of HDDs is hard to predict and unlikely to be much greater than 5 years.