Personally and I do mean personally. I've been using unraid since 2009 and I have had 3 builds using the same USB. The only thing I have 2 of is cases. Everything else has been swapped in and out of 1 case. Motherboard, ram, yadda yadda. So what I did I picked through my pile of goodies and slapped together a second system and purchased 3 x 12TB drives and I'm still using my 6 x 4TB drives in my primary because I can swap them in and out as I need and expand their sizes when ever I need. That doesn't benefit my Backup server stuck at 24TB, but none the less I'm not full yet so I'll have to deal later.
Every day my some files on my Cache are backed up to another SSD in the same machine with a script I wrote which is nothing fancy, but it does what I need to it to. Also every day at 8AM when I know Plex is done doing all of its normal stuff my backup server connects via unassigned Devices to my Primary, backups all my media and other various files then disconnects. Its been running flawlessly for months. I've been meaning to change up the code some so when I turn on the Backup server it performs the backup and shuts its self off, but I keep forgetting. I intend to relocate my backup else where out of the house possibly into the garage hence the turning it on so it doesn't sweat to death or freeze or I might take it out to the shed we are building and insulating. I'm guessing it will end up in the shed honestly since it will be in a better environment temperature wise.
None the less save those old builds. You don't need lots of horsepower to do a backup especially if your primary is your media server or whatever its doing for you.