I was previously using one folder for multiple backups, but it doesn't
help for pruning old backups. So, now, each backup set has it's own
folder, what makes it easier to restore as well.
It appears to be safe enough to have just a few repositories (2 per
disk, 4 at total) to avoid backup corruption and it will increase a lot
the disk space management and how long I will be able to keep my
backups.