3-2-1 has been updated to 3-2-1-1-0 by Veeam’s marketing at least.
At least 3 copies, in 2 different mediums, at least 1 off-site, at least 1 immutable, and 0 detected errors in the data written to the backup and during testing (you are testing your backups regularly?).
At least 3 copies, in 2 different mediums, at least 1 off-site, at least 1 immutable, and 0 detected errors in the data written to the backup and during testing (you are testing your backups regularly?).