How often should back-ups be performed for our organisation?

Therefore, the regularity with which you undertake your back-ups is dependent on two things: the rate of change of your data and practicality.  For example, if you only create one or two new documents a week, then daily back-ups would seem a little overboard.  Possibly a weekly back-up would be more practical.  However, if your daily work involves processing event registrations, cheque payments, logging calls, etc, then an overnight back-up would be a practical minimum.

It is possible to do real time back-ups, where copies of data are made as changes are incurred, and also to store data across several machines for added redundancy. However, all added redundancies and fail-safes carry additional cost.  When deciding on a back-up schedule, a CEO should attempt to estimate how much work (in hours) their organisation could afford to lose before it becomes a big problem.  If you imagine coming into work to the announcement that the server has died, how far back in time are you willing to go to retrieve your data?  Yesterday's back-up or last month's back-up?

Most community and voluntary organisations will have transactional data every day, but will not be handling vast quantities of financial records, so a good standard practical approach would be to perform one back-up every night, with one back-up stored off-site every week.

There is an in-depth piece on the reasons to back-up and the technologies to do so through this link.