This was an old project of mine. A few years ago I had a huge load of data comming in (~4 TiB) and the amount of storage I needed suddenly more than dubbled. Until then I was using two 1.5 TB HDDs which I mirrored by hand using rsync, because I’m paranoid of loosing data. It was annoying to always copy all data to each disk to have redundancy – and certainly not a smart solution. Now that data wouldn’t fit onto the two disks anyway, so it was time to think of a new solution. I had enough of wasting my time with copying files from one hard drive to another.