Data backup should be a vital part of your IT strategy. It allows you to continue doing business even after a disaster strikes. Think of it as like a spare tyre for your car or a liferaft on a boat. You hope you never have to use it but when you need it it must work. So your backup strategy must be well thought out, it needs to make sure you are backing up the information you need as frequently as you need onto a reliable storage media.

Data backup performs two roles. Firstly it reduces the effect of a major disaster such as a terminal hard drive failure. Replace the drive, restore the backup and away you go. Secondly it acts as a saftey net for user mistakes. If someone accidently deletes a document they have spent two weeks preparing you can restore the individual file from the last backup tape.

What to backup? The main thing is your data which should be organised so that it is easily separated from the other files on the system. Data will consist of not only your document files but also any databases and your email store too. Some items such as server databases cannot be directly backed up while on-line so have to be stopped, backed up and then restarted. Then there is the system information such as active directory data and system state. These are important since they document the internal structure of your network including user accounts, access rights, etc. Not as vital perhaps as the data but still a tedious job to recreate if lost. Lastly there is all the applications software installed on your servers. Whether this is backed up or not depends on how quickly you want to be able to return to normal operation following a failure. What is not backed up may need to be reinstalled from scratch.

How often? Your backup strategy should be chosen so that you never loose more data than you can afford to reenter. For example, if you backup all your data every night then the most you could loose is one day's worth of additions and changes to that data. If your data is constantly changing you may want a more frequent backup stategy (there are some things that can be done to help in this situation) if your data changes very rarely then you may only need to backup weekly or even just as and when required. The important thing is to pick a strategy and stick to it. Nominate someone who will take responsibility for making sure the backups are done effectively. Backups are normally done overnight since there is generally less load on the systems at this time.

Which media? The choice of method and media for your backup, like most things, comes down to a balance between cost and requirements. It's a waste of money to go for a £2500 500Gb super fast tape backup system if you only need to backup 10Gb of data. Similarly backing up 500Gb of data on to 50 10Gb tapes is going to be completely impractical. In general higher capacity and higher backup speed mean more expensive equipment and media. If you have a requirement for very frequent backups because of rapidly changing data it may be a good idea to use data mirroring techniques. This is where the data is stored in more than one place on the system. It can be as simple as having a pair of hard disk drives acting as a mirrored pair; each disk holds a full copy of the data and writes are done to both sets at the same time. Or it could be as complex as having multiple servers in different locations each with it's own copy of the data which is kept synchronised with the other servers. Most business systems use a combination of disk mirroring or RAID arrays to provide fault tolerance and a good tape backup process.