Dear All
Backup methods depend on the users requirements.
Other than tape consider these.
Very popular with support people these days are the small size (desktop) USB drives, they are relatively robust compared to earlier models ie they are meant to be portable, so do have a high degree of built in shock tolerance eg from poor handling & dropping, although of course it's better not to drop them.
They are also reasonably cost effective, so you would buy 2 at minimum and swap them each day, or eg buy four disks, one disk for each week, and rotate them weekly over a 4 week period.
The exact cycling depends on your backup needs. If the data must be removed off site every night and retained for a week, then you need five USB drives, and cycle them again next week.
Also not yet mentioned in this thread is Affa. You create a offsite backup server using SME, install and configure Affa, see the Contribs wiki article, and you backup daily (or more often) via Internet connection. It runs unattended (which is a great plus), and you can keep many backups eg for as long as a year (depending on disk size), and restore from whichever date you want to, including single file restores done remotely if required.
The initial full backup is best done onsite, due to the long time it will take if there is a large amount of data on the live server, and then move the backup server offsite & reconfigure accordingly. It is fairly easy to setup. Then affa does daily (or more often if specified) incremental backups of data that has changed.
To do a restore in the event of a major server failure, you deliver or have couriered the server from the offsite location, and "rise" Affa so that the backup server becomes the live server.
Alternatively restore from the Affa server backup to a newly built live server via LAN connection.
Obviously obtaining and building a new server hardware takes time, so the Affa "rise" feature is great for quickly getting a production server running again using the same backup server hardware, until more time can be spent obtaining new live system hardware etc. A typical rise takes about 20 minutes as very little data is copied.
If your remote server is located in the same city then it's only an hour or two to get the backup server couriered to the live site, and 20 more minutes to have it up and running.
It's also good to have multiple backups in case something goes wrong with one backup method in the event of a server crash & critical data loss eg onsite USB drive or two, plus offsite affa unattended backup.
For archiving backups, copy data to DVD's or maybe blue rays disks, there is nothing else really suitable that is cheap except tapes (but the tape hardware is more costly to start with).
Your requirements will for sure vary and the justification for implementing different methods will also vary.
Check the Contribs & Howtos Backup category for other methods too.
I also backup to a removeable hard disk in a workstation, and rotate the disks daily.