rsync is the default way of creating snapshots, and the only way unless you're using
I use the
ext4 filesystem, so
rsync for snapshots is the only option for me.
If you're in doubt, use
rsync. If you're a
btrfs user and know what you're doing, well, then you don't need to ask
How much space should you set aside for snapshots depends on how many snapshots you make. The first snapshot is going to be the same size as your root (minus your home). Any subsequent snapshots are going to be smaller, since anything that is identical between the snapshots is hard linked, saving a ton of space. It's difficult to say how much space you'll need, maybe twice, or three times the size of your root (without home, of course)?
Should it be on the same drive or on a different one? It can be on the same, but it's more convenient if you put it on a different drive, because then you can nuke your root drive and still restore a snapshot. If you're using
btrfs snapshots, they have to be on the same drive, though (there might be a workaround for this, I don't know).