3 x 3TB drives in RAID 5 will get you (almost) 6TB with only 9 TB total capacity, and its more fault tolerant than RAID 1. Also, its cheaper to replace a single 3TB drive than a single 6TB drive, so it’ll spread your costs out more.
I have 4 x 3TB drives on RAID 5, and I got three of them used for cheap at a local computer place. They’ll have lower life expectancy, but unless more than one dies at a time, it’ll be cheaper to replace them as they do. I got 1 drive new, and plan to replace 1 drive every year or two with new.
Unless you need speed, definitely consider HDDs, especially NAS grade. They’re slower read/write, but your use case shouldn’t need a lot of have read/write. HDDs–even the premium ones–are way cheaper than SSDs right now with the shortage, and have great longevity.
Agreed. An old machine with extra drives is both way cheaper and more flexible. A little more work, but nothing you can’t figure out with web searches and forum help.