They are in some phones.. Shop around :)

Speak for yourself. My Motorola g73 has a micro SD card slot.

I think it's primarily targeting the handheld gaming market

Steam games. I want to have all my 50-100 GB games available without having to decide what to uninstall.

Currently I have two 512gb SD cards for my Steam Deck.

If it craps out, it's okay.

My laptop has an SD card slot. So if this were reliable I could add a significant permanent storage capacity to my laptop.

I would happily use one for my music and movies to access them on the go. I already have copies elsewhere, so it would be no big loss if the card died.

If you set it up properly (like using apps to sync folders) a big enough sd is like local "cloud" service.

I was thinking about it recently, after my phone data were very close to being deleted (I managed to prevent it eventually), I was angry at how not having an sd slot caused me so many issues. If I had a 1tb sd I would just autosync app backups and files to my card and not worry ~at all about losing data from bootloops etc.

How the heck do people with 4TB SD cards do data hygiene wipes of their medium before crossing international borders?

They don't

I don't know what your particular situation is but if you're just using it on computers you could use LUKS or BitLocker or FileVault. Then if you want to wipe it, you only need to destroy the key and the data is rendered effectively gone.

I assume you're joking, but if not: the 4MB of flash you see is not mapped 1:1 with 4MB of actual flash on the SD card. Instead there might be something like 5MB, but your OS only sees 4MB of that.

The extra unallocated space is used as spare sectors (sectors degrade and must be swapped out) or even just randomly if it somehow increases IO performance (depending on the firmware).

Erasing the 4MB visible to your OS will not erase everything, there still may be whole files or fragments of your files sitting in the extra space. Drive-vendor specific commands can reliably access this space (if they exist and are available to you, which they mostly are not). Some secure erase commands may wipe the unallocated space but that's vendor specific, not documented and I don't think even supported over the SD interface (although I might be wrong on this last point).

Encryption and physical destruction are your best bets.

The article says 10MB/s minimum write speed, which would take 4.6 days to transfer 4TB, so... yeah. Even with the "max theoretical transfer rates" of 104MB/s (which is probably just read if anything) that's still almost 11 hours.

That's just Micro SD cards.

I doubt they would be reliable enough for a RAID array. It would be much better to use m.2 drives.

You probably don't want it
https://www.youtube.com/watch?v=O2jKKFUnycA
https://www.youtube.com/watch?v=3frnBoqqI_Q

It wouldn't be the best of ideas because the flash used for SD cards do not have the same kind of write endurance as other types of flash media.

More writes, more failures. SD cards work best when you write once and don't delete it for a long time

The ones used for 4K recordings are not slow 100+MBps, I won't say prone to failure as such, flash storage can only handle a finite number of writes but we can mitigate that by using wear leveling.

when 4TB is stressed.