In the week, I got acquainted with the OSX Time Machine’s “Local Snapshots” which get created when your normal Time Machine volume is not available. When digging around for more information on it, I came across the trainee backup-nazi’s standard line that a backup on the same hard disk as the original data is no backup at all, and is completely useless. Well they were half-right.
To over simplify, backups perform two basic functions – they provide a copy of your data that you can use in the event of a disaster (your laptop gets stolen, your house burns down, etc.), and they allow you to recover from those “Oh! I didn’t mean to delete that file” moments. And the later use case is by far the most common – particularly in an organisation where you can ask someone else to recover a file for you.
But of course local snapshots that get created when the backup media is not available are not true backups. Any disaster that occurs is very unlikely to destroy the original data but leave the local snapshot unharmed; if it does leave it unharmed then fine. But backups are for the worst possible scenario – I did not mention your house burning down by accident.
But local snapshots are useful by themselves; whilst they are certainly not backups, they can be very useful for the most common variety of restoration job. And because they are so available, it is possible to use them for purposes we would not have thought of before.
Such as looking at what that document you are working on looked like yesterday. That paragraph you re-worked; does it really read better today than the original version yesterday? In a more technical sense, I have been using file system snapshots for years – to look back in time.