Back in the 1990s, I had to store a large number of digitized photos electronically, and went through all sorts of different storage media trying to figure out what was the most economical, most reliable, and most compact medium. As a result of that, I've been watching various media over the years to an eye for the best thing to use for long term storage. At one time I used a SyQuest drive with removable hard drives (actual hard platters just like in a regular hard drive, but in a cartridge) Those however were rather expensive and each disk was only 120 MB, so it became apparent that it wasn't an economical long term solution.
Fast forward to the early 2000's and I was recording TV Shows. Wanna eat up hard drive space in a hurry? Record a few movies in HD! I had 14 seasons of NCIS stored on my computer at one time, LOL. So again my attention was drawn to finding ways of long term storage that were feasible and economic. And because of those large files on my computer, doing a full backup became a problem (it would take something like 425 rewritable DVDs to do a full backup of just the primary drive, and I have 4 hard drives in the computer). I now back up to another high capacity hard drive.
At one time I thought USB sticks and SD cards were the ticket, until they started failing on me.
I have a very large collection of DVD and CD data disks. Optical media have been more reliable than electronic for me.
But what has been the most economic and reliable is good old fashioned hard drives. (but not the most compact) With a USB hard drive interface, OTG cable, and a USB splitter cable than can draw power from a USB charger, I can plug in a regular hard drive to my cell phone and tablet. It wasn't feasible to store large quantities of data (I'm talking terabytes) on hard drives at one time without a warehouse to hold all of them and Bloomberg's checkbook! But now with high capacity notebook hard drives that are very inexpensive, you can store immense quantities of data in duplicate in a small amount of space at relatively low cost.
The jury is still out on SSDs. They haven't been on the market long enough to know how they will hold up over time. It is possible that they will be the best medium, but based on my problems with memory sticks, I'm not holding my breath.
Thank you very much. The idea of using portable hard drives hadn't occurred to me, and I think it's an excellent idea.
Thank you again.
When I move forward, I'll let everyone know what I decide to do.