Questions answered and problems solved
I have two Mac Pros (the tower case kind). One is getting rather old and will soon be replaced, but the hard disks in it are quite large (500GB and 1TB) and I am thinking of fitting them in the other, which has its own 1TB drive. What is the best way to set these up? Keith Morten Are you actually short of disk space, or just giving the old drives a good home? If it’s the latter, I would counsel against it. This just creates more points of failure and makes your backup strategy more complicated. The simplest system is to have one drive for everything and another drive of at least the same size (ideally a bit bigger) for Time Machine. If you don’t already have a Time Machine drive then I’d use the 1TB drive for this and dump the 500GB. If the Mac Pro you use is already adequately backed up and you don’t urgently need more disk space, then I wouldn’t bother at all.
If you are short of disk space, then you could install the 500GB drive for your data and use the other 1TB disk as its Time Machine backup. This will allow you to keep lots of backups of the data files.
I’d still favour replacing your existing disk with one large enough to hold both apps and data (and another to back that up) rather than reusing old drives. Hard drives older than five years have a much higher failure rate so it is rarely worth reusing them, unless your budget is very tight.