Warning on the dangers inherent in trying to use SD cards as your "permanent storage" medium!

Not much more to say on this - except READ THIS !

Do SSDs have the same dangers?

Many opinons on that question (just "search")!

OTOH, most "quality" SSDs have a quoted "write/read" life in "large numbers" that will (probably!) never be exceeded by most "home users" - but, Yes, they do degrade/fail over time (and thus you need to keep an eye on the "health" App that can be installed with most of them), but almost certainly not anywhere as "poor" as SD cards which are designed for much lower write/read cycle numbers.

OTOH2 - bought a very cheap "no-name" and non-standard physical size bare-board SSD to fit a small and "weird" ACER N4620G nettop which had a special connector - worked fine for a few weeks until a large W10 "update" download and install resulted in the processor being totally fried due to overheating after the install process seems to have "looped", which I can only blame on that SSD

It seems from my searches that I'm best off sticking with hard drives for longer term image storage and even they have a considerable chance of failing after some years.

Another solution would be to get something uploaded to the 'cloud' but I don't know how much I can trust that. I suppose I can also print my favourite images so I can hold onto a physical copy. I'm sure that'll also degrade over time and lose some colour.

I don't store images on SD cards on purpose, but occasionally require an old card for reuse and have found images on them still intact after a good few years. I've had more issues with memory sticks failing.

Don't rely on cheap CDs either. They can become unreadable after a few years. Some of my home made music CDs now sound worse than bad 78s!

Backing up computer data is a huge topic and a very complex one. Hard disks aren't safe, they do and will fail, SDDs are too new to tell, as with anything there will be more reliable disks and less reliable ones. Multiple disks reduce the risk but are a pain to maintain. The most reliable option today is paid for cloud* storage (which does all the messy stuff for you), this does introduce potential security & privacy issues though. Cloud storage also needs good internet bandwidth if you're uploading lots of big files (i.e. large TIFF files).

My experience with SanDisk SD cards back to 2012 (and earlier for CF cards) is that I haven't had a failure. I recently moved contents into the cloud from SD cards untouched since 2012 without issues. I format them in camera, use them until almost full (deleting a few images in between), then put them away (the less you handle them the safer they are). They don't like any bending loads or damage to the contacts.

The OP of the Pf link at the top seems to be using the camera as a card reader & TV display, putting the cards into multiple camera types. If this is routine (as it sounds), this handling is likely to damage the cards or card slots in the camera. Apart from damage to the cards, there may also be file format issues between different cameras (I wouldn't expect a K-5 to open a K-3 image). As mentioned, always lock the card before reading it in a different card reader. Some PC systems try to write their own data as soon as it goes in - which a camera may not like.

* Note: By cloud storage I mean a generic computer data cloud store, not one of the photo sharing platforms that limit size or file types. I don't mean Adobe CC although that may suit your workflow.

We regularly replace SD cards, as file sizes have become bigger we've moved from 1GB cards to 16BB or 32GB on our journey since the *istDS. Only one became a problem, not reading in one K-5 but reading in another K-5. Images were downloaded and the card discarded.

The cost is very low to keep up replacements every couple of years, but they are only used for short term storage and always formatted when re-used. so problems have been few and far between.

Another thing for people to remember about "storage" media - if you bought a new laptop (or even a desktop/tower PC) in the last couple of years, the main on-board storage was almost certainly an SSD as HDDs (and DVD/CD drives) in most of them are "history" (and there isn't space inside to fit them anyway - that's why most newish laptops are so light!)

I think the best approach is to have a solid backup regime.

My picture files are on my computer (desktop) hard drive. This gets backed up to a permanently plugged in separate hard drive once every few months. I further back up to another plugin HDD drive once every six months or so.

Similar to Peter, other than none of my images reside on my desktop, they all sit on 3 separate hard drives and backed up after every major shoot and if we go away, I take one with me and a neighbour looks after one as well.

4TB ssd Thunderbolt 3 (4x 1tb ssd stripped 0 raid).
8tb (2x4 tb hard drives in raid 0) usb3 enclosure
4x 4 tb hard drives in a mediasonic usb3 enclosure
16 tb usb raid drive (4x4 tb drives).
for photo and video editing, storage and backups locally..
also 8 tb NAS for backup the computer and archived off site storage on 8 tb back up drives.

I guess if your data is worth anything to you, spending as much on storage and backups as you do on computers and cameras makes sense... I don't erase the memory cards until I have three copies made on different drives.

The benefit of proper cloud storage is it doesn't cost anything to set it up, it costs a few cents per Gb per month on AWS and they handle everything else. Self hosted hard disc farms are rapidly becoming a thing of the past.

Until, of course, one factors in the ongoing longterm yearly payments that have to be paid to maintain it "ad finitum"?

OTOH: the "challenges" of seting up and maintaining one's own "local storage" is a "stimulating" one

Another issue with cloud storage is that the company providing it might just stop doing so with little or no warning! Or you may miss a payment or two and loose access. BTs cloud storage systems have gone through several incarnations which were simply dropped and replaced. I wouldn't trust another with anything important.
I did notice Google seem to automatically back up any photos on an android phone to their servers whether you like it or not.
The normal recommendation is to keep incremental backups and an off-site backup of important data and schedule to update that too. I doubt many home users do all that though.