As explained in How Computers Work it is amazing that computers work as well as they do, but they all fail eventually.
The single most important function you can perform with your computer is to backup your data.
I first learnt this lesson when I wrote programs (using BASIC code and Z80 machine code) on a Sinclair ZX Spectrum. It took many hours cramped over the fiddly little rubberised keyboard to fill the puny 16KB (KiloBytes) of RAM (Random Access Memory), and many more hours tweaking to make it work. Anyone else who tried this knows that the power connector was pretty flaky, and a single wrong move could see all your hard work consigned to the ether and the screen filled with a gaudy patchwork of digital garbage. It wasn’t much easier playing the contents of the RAM down an audio cable into a borrowed cassette player, but we learnt to do it every time we had something we wanted to keep. I have not lost a single byte of data since.
There are three factors to consider when choosing a backup strategy:
The primary aim of a backup is to restore all of the chosen systems and data to their original state and function as quickly as possible after a failure. In the case of a mobile telephone this is quite easy - you can just have a spare phone and a copy of your SIM (the memory card). With a personal computer it is a bit more complicated:
The most important thing to backup is your documents - they have been created (or collected) by you and it would probably take a long time to rebuild them by hand. Most of these files will be found in one of several standard locations (the My Documents folder and the Desktop). You might also want to backup your emails, photographs, music and various other program data and settings. It can get complicated and there is always the risk that you have missed something important.
It is much simpler to backup all of the files on your hard disk drive (usually the C: drive, but you might have multiple hard disk drives). Of course this takes up more space and might influence the backup timing and location (you might need to backup less often, keep backups for a shorter time, or use more and larger media for backup storage).
Some files on your hard disk drive cannot be copied while the computer is running because they are in constant use. These include some important files such as email and other program settings and data. These files can only be backed up using special software or hardware, such as a RAID (Redundant Array of Independent Disks) controller, Windows Backup or other specialised backup software.
Backups can be scheduled or manually initiated. A backup to an optical disk (CD or DVD) is usually run manually, whereas a RAID controller usually runs continuously. A backup to an external hard disk may be either scheduled or run manually.
Obviously the more often you backup the better, and ideally you would backup a file every time it changed. The more often you backup, the less data will be lost when a disaster happens. For example, if you backup every ten minutes, you only stand to lose ten minutes of data. Conversely, the less often you backup, the more data will be lost, and if you only backup once a year, you stand to lose up to a years worth of data.
In practice you should backup each time the contents have changed significantly. This depends on your workload and how much value you place on that work. The backup frequency is related to the backup device: a RAID controller will backup continuously and instantaneously, whereas you might backup files to an optical disk (CD or DVD) only once a month.
Obviously the longer you keep a backup for the better, and ideally you would keep a backup forever. The longer you keep a backup for, the more chance you have of retrieving an old version of a document, file or system. The shorter the duration of the backup, the less chance of retrieving that old version.
In practice each backup should be kept for an appropriate length of time. For example, if you perform a monthly accounting process it would make sense to keep backups for at least one month. If you process legal or financial documents, you may be required to keep backups for a long period of time. The backup duration is related to the backup device - an optical disk (CD or DVD) is cheap enough to put in a safe place and keep forever. On the other hand, a RAID controller will backup continuously and instantaneously, so the duration of the backup is exactly the same as the duration of the original file, and you cannot recover old versions of files.
| Strategy | Device | Device Type | Media | Media Capacity | Backup Frequency | Backup Duration | Protection |
|---|---|---|---|---|---|---|---|
| Archive your documents to an optical disk (CD or DVD) once a month | Optical Disk (CD or DVD) Drive (Writer) | Internal or External | Writable or Rewritable optical disks (CD or DVD) | 500MB to 50GB (Dual-layer Blu-ray) | Monthly | Forever | If the backups are stored in a different location to the original data it is protected against virtually all disasters. You can retrieve documents from monthly intervals in the past, but you might lose up to one month of data between backups. |
| Use a RAID array to backup the entire system continuously and instantaneously | RAID Array | Internal or External | Hard disks | 10GB to 500GB | Instantaneous | Same as file | A RAID array is a collection of hard disk drives containing multiple copies of your entire system. If a hard disk drive fails, it does not affect your data and can simply be replaced. You are protected against the failure of one hard disk drive, but you are not protected from any other type of disaster. Any changes are written to all copies of the data immediately - you cannot retrieve historical documents. Also, all the hard disk drives are in the same location, so a physical disaster like lightning, fire or flood might damage all copies of the data. |
| Backup your entire system to an external hard disk drive every day, keeping 5 separate copies | External Hard Disk Drive | External | Hard Disk Drive | 10GB to 500GB | Daily | 1 Week | You are protected against the failure of a single hard disk drive, whether it is your main internal hard disk drive or the external hard disk drive. You can retrieve any file from any day in the past week, but you might lose one day of data between backups. If you make the backup during the day and keep the unit off-site during the night, then you have partial protection from physical disasters - you are protected from physical disasters during the night, but not during the day. |
| Backup your entire system every day, spread over several external hard disk drives, keeping a total of 30 copies | External Hard Disk Drives | External | Hard Disk Drives | 10GB to 500GB | Daily | 1 Month | If you rotate a sequence of external hard disk drives between the backup site and another safe site, and spread 30 complete copies of your system over these external hard disk drives, you are protected against virtually all disasters. You can retrieve any file from any day in the past month, but you might lose up to one day of data between backups. |
Using a combination of strategies you can protect your computer system from all potential disasters, and make a number of previous file versions available from various points in time. For example, if you backup using a RAID array, a monthly archive of documents to an optical disk (CD or DVD) and a complete system backup on a rotation of external hard disk drives, then you are unlikely to ever lose a significant amount of data. This might sound like a lot of effort, but all of these solutions are easily implemented by a small business, and will pay for themselves many times over in the long run...