Heya,
I'm thinking up front, it's important to distinguish between simply having uptime hardware and solutions compared to backups at the archival level. I don't think all data deserves archival class treatment, only data that will need to be available in the long run, so archival class media, true backup solution, likely is rather different for most people compared to their solutions for simply having good uptime on their active data. An example being, some software today may not be at all useful to have a backup of in 10 years, but your family photos or archived photos for your research (think microscopy, astro, etc) may be something you wish to survive 20~30 years, or more, without constant refreshing onto newer media every few years. Or insert any example of data that you might think is important enough to keep long term and might actually need to be accessed by someone one day. I also think anything that is a true backup or archival class backup needs to be so simple that nearly anyone can recover it (unless its sensitive of course). Meaning, I think a medium and file system that is going to be relevant and common that future hardware can handle it. An example would be today's hardware is still commonly able to read a CD-R from the late 1990's with your JPG's and TXT files on there no problem, despite the drives changing from IDE to SATA, and several revision. But the optical platform never went away despite it's popularity shifting to two different mediums (DVD-R and BD-R, etc). So extrapolate another 20~30 years with DVD-R and BD-R to whatever is the future, I would assume optical drives are still going to be relevant, even if for nothing more than archival purposes.
So for current active data sets, I'm thinking modern HDD or SSD in a system with redundancy is the first line of defense for creating uptime. This could be in the same system, or two separate systems, such as a living set of drives in your primary system being used, that is also copied onto a separate system, such as an external drive system, or network attached storage, with the ability to have redundancy, such as mirroring or for some using various parity systems. This allows the lowest cost per capacity drives to be used with modern speeds, because redundancy gives you that little room to have a fault or failure and still have a living data set at your immediate disposal. Some may use RAID systems. Others may favor the ZFS file system. Or something else even. I think the less exclusive hardware needed, the better. And I think if the file system itself has data checking and validation as part of it is also good (like ZFS). The argument for HDD vs SSD is mostly going to be cost and capacity related, as the HDD is still the cheapest cost per capacity but has shorter lifespan and needs recycling more often; the SSD has higher cost per capacity, but has longer lifespan in a working environment and needs less frequent recycling, but ultimately still needs to be refreshed eventually (10 year being a maximum likely).
The second set of data separate from the above primary active data is likely still not a backup, but rather simply something that supports uptime via redundancy in the form of having separate physical copies on separate media. Some do this on Flash media or solid state media, but this is only good for short term and only for low capacity needs. Some do this with HDD or SSD in hot or cold storage systems depending on their setup and is still only good for short term. The most common high capacity thing would be an external HDD with access via eSATA, USB or Network. The most common low capacity thing would be the flash solid state memory modules that everyone has laying around. And then there's the massive capacity needs with redundancy as another option, such as having a second NAS with mirroring or parity built in for a generous support of uptime having two completely separate systems with the same data both with independent redundancy systems. While this is still not a backup, this is a nominal uptime strategy for someone at home at least and still affordable enough to do.
Everyone gets to that point I think, above. Figuring out if external HDDs are ok for your needs. Or if some Flash sticks handle most of your small needs. Or maybe a little bit of Cloud use for stuff that's not high capacity and/or super sensitive information. For some, the living data is likely not redundant in the primary system and the external HDD or NAS is the secondary set of data with or without redundancy, which is still a total redundant system. It's getting to that third level that we start to enter the idea of a true backup or archival medium and system to allow for greater redundancy and not just uptime. Ie, can it survive 20 years in a vault somewhere and be usable with access from future hardware and in container and file systems that will not require specialists or VM's just to access them.
I don't think HDD, SSD (at least yet), Flash solid state, nor cloud services really do this justice. Even with redundancy. Everything has a compromise in some way. So it's important to figure out if your data is worth the cost, compromise and complexity and what system will work for your needs.
For example, when I think of a backup, I think of the following:
Will the medium itself survive 20~30 years in cold storage?
Will the medium have hardware to access it in 20~30 years, or more?
Could this system be refreshed and migrated to new mediums in 20+ years?
Will the file system and/or containers be universally accessible in 20~30 years without legacy hardware/software?
Can someone other than yourself retrieve this data without advanced knowledge of all of this hardware/software (ie, can you stroke out and your family get the data)?
Will the encryption be needed or will it be worth risking loss if needed if you were to become unavailable or lose that key in 20~30 years?
Will the medium survive common risk stuff (flash house fire, water damage, crush damage, etc)?
Will the system be subject to ransom online (where you really need it encrypted to avoid host snooping; and will this system survive 20~30 years anyways)?
For anecdotal argument, here's my experience with this:
I have no surviving portable media like floppies or zip discs, etc, from the 90's.
I have no surviving HDD's from the 90's (IDE/SCSI connections, etc; yet notice the power coupling is still available today over 30 years later!)
I have no flash surviving from the early 2000's (though USB has retained compatibility for its existence).
All my data from the 90's that I've kept has migrated over time to new hard drives over time (I physically moved to new drives).
I have CD-R's I burned in the late 90's that are still accessible and today's modern hardware and OS reads them fine without anything legacy!
I have DVD-R's I burned in the late 90's and early 2000's and they're still accessible and again today's hardware uses them without any legacy!
So I'm thinking from an archival class, true backup point of view for my purposes, optical is likely the way to go for backing up data that I want accessible by a third party in 20~30 years on common hardware without any special software needed in common containers and file systems. And today it's likely BD-R centered in some way.
The idea being, if I back up important data, like images (RAW, JPG, etc), research images, plain text documents of critical information, legal stuff in PDF or TXT or DOC, onto optical media with simple structure (ie, UDF, ISO, etc, FAT based or EXT based, etc) using folder names and file names without needing meta data just to know what you're looking at, that can be tucked into a safe that can survive flash fire and some flooding or even stored off site somewhere to increase redundancy, and in 20~30 years when I stroke out or have a heart attack, my kids or grandkids even, or another relative or even a friend could be handed a box of optical discs and they not even know what they are can look at them and figure it's an optical disc and inserts it into some common readers in their day and it actually simply spin up and work. Just like I can access a CD-R from the 90's today with my common modern hardware, 30 years later.
Thoughts?
Alternatives?
How would you approach this concept?
Very best,