Backups and recovery

A backup is a copy of data stored separately from the original, so that the original can be restored if it is lost, corrupted or damaged. Recovery is the process of restoring that data from the backup.

Backups matter after a major system failure — a hard drive that stops working, a ransomware attack, a fire in the room where the server stood, or a folder someone deleted by mistake. Once the fault is fixed, the backup is copied back and people can carry on working.

Automatic and manual backups

Many systems back up automatically on a schedule, such as every evening at 11pm. Nobody has to remember to do it, and at worst the work done since the last backup is lost. A manual backup is started by a person at a chosen moment, often just before a software update or a hardware change. Changes like these can go wrong and leave a system unusable, so a fresh copy taken beforehand means you can put everything back as it was.

Storing and testing backups

A backup should be kept securely and separately from the original data — on a different drive, in another building, or with a cloud service — and access to it should be limited to the people who need to restore it. A copy stored on the same disk as the original is no help at all: one failure destroys both. Backups should also be tested by carrying out a practice recovery, because a backup that turns out to be incomplete or corrupted is only discovered when you desperately need it.

scores = {"Amara": 12, "Ben": 9, "Cerys": 15}
backup = scores.copy()   # a separate copy kept safe

scores.clear()           # the original data is lost
print("Original now:", scores)

scores = backup.copy()   # recovery: restore from the backup
print("Restored:", scores)

Output:

Original now: {}
Restored: {'Amara': 12, 'Ben': 9, 'Cerys': 15}

A backup does not prevent a threat from happening. Malware will still infect a machine that is backed up every night, and a thief can still steal a laptop. What the backup does is let you get the data back afterwards.