Friday morning, the disk is dead
A design studio makes a backup every night. On Friday morning the main disk fails.
How many copies must the technician put back before the studio can work? The answer depends on the kind of backup.
One kind needs four copies. Another needs two. You will see why.
By the end of this lesson
Note
I can work out which copies to restore for each backup type.
Key words
| Word | What it means |
|---|---|
| Full backup | a copy of all the chosen data |
| Incremental backup | a copy of what changed since the last backup of any kind |
| Differential backup | a copy of what changed since the last full backup |
| Mirror backup | an exact copy of the data at one moment |
| Immutable backup | a copy that nobody can change, overwrite or delete |
| Restore | to copy backed-up data back into use |
| Ransomware | malicious software that locks your data until you pay |
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3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Five types of backup
A full backup copies everything. It is big and slow, but it is easy to restore.
An incremental copies only what changed since the last backup. A differential copies what changed since the last full one.
A mirror is a copy of the data at one moment. An immutable copy cannot be changed or deleted, even by an attacker.
The five types side by side
| Type | What it copies | Good point | Weak point |
|---|---|---|---|
| Full | All the data | Simple, quick restore | Big and slow to make |
| Incremental | Changes since the last backup | Small and quick to make | Slow restore: many copies |
| Differential | Changes since the last full | Restore needs two copies | Grows bigger each day |
| Mirror | An exact copy at one time | Quick to use | Mistakes and deletions copy across |
| Immutable | Any data, locked for a time | Safe from ransomware | Cannot be removed early |
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3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.