The purpose of backups is to enable you to rebuild the system if necessary. You must weigh all decisions about backups with this in mind. You should consider at least the following points (note that they influence each other to some degree):
- How paranoid to be?
How much do you trust your system? Can you get the software (operating system, applications) from elsewhere quickly and reliably enough, or should you keep local copies? Can you get compatible versions? Will you be able to use the same hardware and software to restore? What disasters do expect? Do you care about unexpected disasters?
- What to backup?
Can you get compatible copies of the software from elsewhere, whenever you need them, or should you keep local copies? Will it be easy to re-install, or should you backup your complete system?
Important things to remember are non-files, such as the partition table, boot sectors, hardware setups, and well-hidden files, such as many configuration files.
- How often?
How much and how often does your data change? The more often it changes, the more often you will need to back up.
- What media to use?
A good backup media is reliable (it won't fail) and portable (it will work on other machines as well).
- What tools to use?
A good tool is reliable (will detect and correct errors in the backup medium) and portable. It should also be convenient and efficient to use.
- How to verify?
How much do you trust your backup medium? It's hardware, it too can fail. The backup tools might not work correctly, or you might be making a silly mistake using them, so you'll have to verify your backups, i.e., check that they work correctly.
- How to automate?
Backing up can be quite tedious, and that makes them unpleasant to do. If you can automate the process as much as possible, it will be much more reliable and, most importantly, it will be done.