Vulnerability of data (Data Backup)
Data is vulnerable in many ways:
- The system on which it is stored can fail. For example, a hard drive may crash due to component failure.
- The medium itself may become corrupt. Where data is stored on a magnetic medium, this can become corrupt due to a number of factors including moisture, heat, magnetic fields and electromagnetic radiation. Even optical storage which is highly reliable should never be regarded as infallible.
- The system can be stolen.
- The system could be physically damaged through war, criminal activity, vandalism or carelessness.
- The system could be damaged as a result of a natural disaster such as a flood, fire or earthquake.
- The data could be deleted or changed through criminal activity, vandalism or carelessness.
No matter what care you may take to protect a system, additional copies of data need to be made and stored on a regular basis. Copies of data are referred to as backups. The following are some guidelines to working with backups.
- Once backups have been created, they should be store in a secure area at a different site. Never keep backups on the same site as the system. They could be stolen or destroyed along with the rest of the system.
- Backups should be made on a very regular basis. Even for a small organisation, this should be done daily. Even the loss of a single day's work would be a major problem. In large organisations backing up may take place on an on-going basis. A schedule of backing up should be clear policy and adhered to.
- More than one copy of data should be made. If the data is very valuable, the different copies could be stored in different secure locations.
- Different versions of the backup should be retained. The following is an example of a backup schedule that could be followed.
The cycle of backing up starts on the first Monday of the month. At the end of each day of the week a backup is made. At the end of the week, there is a Monday, Tuesday, Wednesday ... Saturday backup. On Sunday a backup is created and labelled week 1 backup. This is kept for the rest of the month. The weekday tapes are then reused and the process repeated. At the end of the month you end up with a series of weekly backups. The last one becomes the backup for the month and the process starts over the next month. At the end of the year you then have a series of monthly backups.
- An appropriate medium for backing up must be used. In the case of companies this would generally be done using tape, although optical storage is becoming more common. For personal use, a CD or DVD makes an excellent backup. DVD writers are still quite expensive. Never use diskettes for backup purposes. They are not reliable for this purpose. Even when backing up a PC, makes multiple copies and keep them at another site for safe storage. You could, for example, use a safety deposit box at a bank.
Often a network server has two identical hard drives, one being a mirror image of the other. This means that if one fails the other one can take over. In other words all the software on the first is identical to the software on the second.
Software can be backed up by making a copy of the cd/dvd media and then storing the originals and using the backups to install from. This is allowed by most software manufacturers. The original is kept under lock and key along with the licence numbers.