I recently started an unorthodox backup strategy that I hope will be a good balance between mitigating data loss and staying on a budget. I currently have terabytes of data that I want backed up, but I haven't found a backup solution within my budget. Cloud storage is expensive, especially after Google jacked up the GSuite costs, and I don't want to pay hundreds of dollars each year for cloud storage on top of what I'm backing up locally. I recently saw an auction for 65 1TB SMART tested hard drives on eBay. I threw $60 at it and ended up winning! The seller is local, so I only paid $65 total with pickup. I also picked up a Lenovo ThinkServer TS440 for $28 on another auction. It has RAID and 8 bays that I can populate with drives.
With this hardware, I'm planning to do a sort of modified 3-2-1 backup strategy. I plan on using the drives that I think will be most reliable in my server (least amount of powered on time, no SMART warnings whatsoever), which will be used as my NAS. Since I have a bazillion drives to work with, I also plan on mirroring a bunch of them to store the stuff that I think is most important and stick them in storage. These will be kept in storage most of the time, so I'll probably write to them about twice a year. With all the drives I have, I could afford to make 2 or 3 mirrored copies without running out of storage. I'll also pick the drives that I think should be the most reliable that are left over from those selected for the server. While these could have a bit more powered on time, having multiple mirrored copies should give me a good enough safety margin for drive failures.
Lastly, I'll still use cloud storage for the most important stuff, but I should be able to keep the costs down by not including everything. This will serve as my offsite backup. While I have terabytes of data that I want backed up, my local backups should be enough for some things (e.g., movies). I could even do another offsite backup with some of my mirrored drives if I want.
Now, I know that used hard drives won't be the most reliable storage and backup solutions, but I think I will have enough redundancy to account for the inevitable drive failures. It might not be 100% foolproof, but it should allow me to prioritize the stuff that I am most concerned about having backed up, while also allowing me to have a good enough backup solution for the remaining stuff. So far I've run Smartmontools on 17 drives and they all show up as PASSED on their SMART tests. It looks like one of these might be failing, as one of the tests suggests that it might have some bad blocks, but I wasn't expecting 100% of them to be useable. Some of them have 4 or 5 years of powered on time, so they will go to the bottom of my estimated "reliability" list. I could probably find a use for the least reliable drives to save some wear and tear on the better ones. For example, I throw music files on them and attach them to a Raspberry Pi or an old computer to serve music from. Since those files will already by backup up elsewhere, I could just use the less reliable drive until it fails.