The Generation Game.
The ultimate backup, of course, is a hard paper copy (or two), since some hardware problems can destroy data on all your disks, whatever you do. However, keeping several copies of each of your disks is prudent and more efficient.
The "grandfather, father and son" cycle of backing up disks is a good way to ensure that you always have a recent copy of your data in case anything goes wrong with the disk on which you are working. This means keeping three sets of disks, and at any time using only one disk of each set (the "son") while keeping the others as backups.
When you make changes to your working disc (the son) use the "grandfather disk" of that set to make the backup on, copying from the son onto that disk. This disk then becomes the new "son" as the next working disk. The old "son" becomes the new "father" and the old "father" becomes the new "grandfather". So, with each backup every member of the family moves to the earlier generation. Keeping just one backup doesn't cover you against problems that may arise or come to light when making the next backup.
Last revised: 10th August 1999