Two ways to save a diary
Aisha copies her whole diary every night. Ben only copies the pages he wrote today.
Aisha uses a lot of paper but finds anything fast. Ben saves paper but has to gather many bundles to rebuild the diary.
That is the choice behind the four kinds of back-up.
Key words
| Word | What it means |
|---|---|
| Full back-up | A copy of everything in the source. |
| Incremental back-up | A copy of only what changed since the last back-up of any kind. |
| Differential back-up | A copy of everything that changed since the last full back-up. |
| Mirror back-up | A live copy that always matches the source, with no older versions kept. |
| Back-up set | One saved copy, such as one full or one incremental file. |
| Restore time | How long it takes to get the data back. |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can describe the four types of back-up and work out what is needed to restore from each.
Starter: the plan
Have a go
Starter: the plan
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Cycle 1: full and mirror
A full back-up copies everything. It is the easiest to restore: you need one set. But it takes the most time and space.
A mirror is a copy that always matches the source. It is fast to switch to. But it keeps no history. If a file is deleted or damaged by mistake, the mirror soon copies that too.
Cycle 2: incremental and differential
An incremental back-up copies only what changed since the last back-up of any kind. It is small and fast. But to restore you need the full set plus every incremental in order.
A differential back-up copies everything changed since the last full back-up. It grows each day. To restore you need only the full set and the latest differential.
Check: which type?
Have a go
Check: which type?
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.