Your phone falls in the sea
Your phone falls into the sea. It is gone.
What do you miss most? The phone, or the photos? You can buy a new phone. You cannot buy back the photos.
A company has the same problem, with data worth millions. The answer is a copy kept somewhere safe.
Key words
| Word | What it means | Example |
|---|---|---|
| Backup | A copy of data kept in case the original is lost. | photos saved to the cloud |
| Full backup | A copy of everything. | every file, every time |
| Incremental backup | A copy of only what changed since the last backup of any kind. | just today's new files |
| Differential backup | A copy of everything that changed since the last FULL backup. | all changes since Sunday |
| Restore | Put the data back from a backup. | copy the photos back |
| Offsite | Kept in a different place from the original. | a copy in another town |
| Air gap | A computer or copy with no connection to any network (linked computers). | a disk in a locked drawer |
| Ransomware | Harmful software that locks your files and asks for money. | a note that says pay us |
| Encrypt | Scramble data so only people with the key can read it. | a locked backup |
| Firmware | Software built into a device. | the code inside a router |
| Driver | Software that lets the computer talk to a device. | a printer driver |
The cells students fill in are left blank in this preview.
Quick check: which backup?
Have a go
Quick check: which backup?
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Three kinds of backup
| Type | What it copies | Time to make it | Space it needs | Time to restore |
|---|---|---|---|---|
| Full | Everything | Longest | Most | Fastest: one piece |
| Incremental | Changes since the last backup | Shortest | Least | Slowest: many pieces |
| Differential | Changes since the last full backup | Medium, and it grows each day | Medium | Fast: two pieces |
The cells students fill in are left blank in this preview.
Worked example: a week of backups
| Night | Full each night | Incremental | Differential |
|---|---|---|---|
| Sunday (full backup: 100 files) | 100 | 100 | 100 |
| Monday (10 files changed) | 100 | 10 | 10 |
| Tuesday (10 more changed) | 100 | 10 | 20 (Monday plus Tuesday) |
| Wednesday (10 more changed) | 100 | 10 | 30 (all three days) |
| To restore on Thursday you need | 1 piece | 4 pieces: Sunday, Mon, Tue, Wed | 2 pieces: Sunday and Wednesday |
The cells students fill in are left blank in this preview.
Safe storage
data-callouts.important.label
Keep at least one copy offsite, so one fire or one thief cannot take every copy. Lock the copies away and encrypt them, so a stolen copy cannot be read.
Extra: The 3-2-1 rule
data-callouts.tip.label
Keep 3 copies of your data. Keep them on 2 kinds of storage, such as a disk and the cloud. Keep 1 copy offsite. Then a fire, a thief or a virus cannot take every copy.