Suppose you burn your CDs to a flash drive. How long do they last? Or external hard drives?
Just checking a few online pages, there’s a level of comfort that a properly stored USB will be readable after a decade and probably longer, but the limiter seems to be the number of write / erase cycles and initial material quality. So archiving onto a new high quality brand-name USB will probably be wise, more than on the novelty banana-shaped one that you’ve used off and on for a few years.
Others have covered it well, but archiving means making a comprehensive copy, with any metadata needed to make sense of it, and keeping it safe, which also means necessarily migrating it to new media and thinking about long-term readability. In that process there is always going to be unvoidable data format loss, but also bit-by-bit risk of irreparable data corruption during the transfer process. A serious data archiving may do two copies and then compare to pick out any glitches.
I do wonder how long a USB stick or SSD will hold a valid copy. After all, is 10 years an acceptable archive limit? most discussions talk about how many writes the SDD goes through, but with archive, it’s the opposite. The contents sit undisturbed after being written for extended periods, so how long will that cell retain its setting? Is it worth putting a USB stick in a time capsule, for example?
By contrast, how long will a regular HDD last? I supposed, barring hardware failure, is the risk that the HDD disk media will lose its magnetization, or that the the emulsion will start peeling… Whereas with CDs and CDR’s, the question is just the oxidization and peeling and for CDR’s the stability of the dye.
Every few months, I do a full backup of critical files - My Documents, music, ebook library, and my digital photos going back to 2001. I have copies online plus a removable HDD and a removable SSD. Fortunately, I’m not into home video, so that particular form of storage inflation is not relevant.
My advice to anyone who asked was - get two sets of media, whether USB or SSD or HDD -make a copy on both. Be sure they are offline. Check every so often as you back up to be sure the media still reads (How important is it that your data be up to date? That’s how often to backup.) If one of your media is showing errors, replace it and make a fresh copy.
you may never want the photos from Uncle Jack’s visit or your trip to Vienna, but if you do, they will always be available if you back things up. Who has print photo albums any more? If they’re on your computer, you can print them any time.
As for online backup - you get what you pay for. Microgoopple Online Backup Storage or whatever may be free for now, but you get what you pay for. The service could disappear tomorrow Worse yet, if it gives you a warning beforehand - do you want to shepherd downloading gigs, possibly terabytes of data, and find a place to put it on short notice? Best case, online storage should be your second form of backup, not the one you rely on.
I worked with some clients who had online backups and crappy internet. OK, your server has a 2TB of data and you made an image backup online. What if a plane crashes into your building and your servers are gone? (Or a beer truck takes out the server room…) Even if you can get a replacement PC the next day as server, can you download 2TB in a reasonable time? Reliably? How often do you do another full backup, instead of relying on an additive stream of incrementals?