2. Making Back-ups
2.2 Full, Incremental or differential backups
There are essentially three types of backup:
Full back-up – this is where you make a copy of all the relevant files (often the compete contents of a hard drive or folder system) and then subsequently make a new full back-up of that data. This process can require a large amount of data to be copied at the time of back-up each and every time.
Suggested media: CD/DVD/external hard drives
Incremental back-up – This consists of first making a copy of all relevant files (often the complete contents of a hard drive or folder system) and then making incremental back-ups of all the files which have altered since the last back-up. Thus, the original back up remains as is, but any changes to files are later added. Thus to restore a file system both the original back up and the updates need to be used.
Suggested media: CD/DVD/cloud storage
Differential back-up – This preserves the original backed up files as they are except where differences are found between the back-up and the original version. As changes to your data are generally few (i.e. you might have added to one or two files only in your file system) there is no point completely redoing the process of backing up files which haven’t changed. Thus in differential back-up only files that are noted as different are updated.
Suggested media: external hard drives/cloud storage
The UK Data Archive suggests NOT overwriting old back-ups with new ones. This is good advice but not always possible for practical reasons (such as hard drive space). Thus, consideration needs to be made of how often a back-up is replaced (i.e. you might wish to hold two back-up versions at any given time).