By the end of this lesson you will be able to
- List at least five ways that data is lost.
- Explain the difference between a backup, a sync and a second copy on the same drive.
- Compare local, external drive and cloud backups.
- Describe the 3-2-1 idea and what version history adds.
Every storage device will fail one day, and a laptop can be dropped, lost or stolen. The question is not whether you will lose something, but whether you will lose something you cannot get back. A backup is a second copy kept somewhere else, and it is the single most useful safety habit in computing. This lesson explains how data goes missing and which kinds of copy protect you from which kinds of loss.
How data is lost
Most people imagine a dramatic crash. In practice the commonest causes are ordinary. Knowing them tells you what a backup has to protect against.
- Accidental deletionWrong file deleted or overwritten
- Device failureDrives wear out, often suddenly
- Loss or theftLeft behind or stolen
- MalwareRansomware locks your files
- Physical damageWater, drops, surges, fire
- Software faultsCrashes and bad updates
Read this figure as text
A gallery of six icon cards, each showing a common cause of data loss.
Six cards. First, Accidental deletion: you delete or overwrite the wrong file. Second, Device failure: the drive or its electronics stop working with no warning. Third, Loss or theft: the laptop is left on a bus or taken. Fourth, Malware: ransomware locks your files, or other malware damages them. Fifth, Damage: water, a drop, a power surge or fire. Sixth, Software faults: a crash or bad update damages a file or the system.
Accidental deletion is the most common loss of all, and the one most people can fix themselves if they act quickly (check the Trash or Recycle Bin first). Device failure follows. A hard disk contains moving parts that wear out. An SSD has no moving parts, but it too can fail without warning. Ransomware is a kind of Malware that scrambles your files and demands payment: the only reliable cure is a clean backup that the malware could not reach.
What a backup is, and what it is not
A Backup is a separate copy of your files, kept so that you can get them back after a loss. The key word is separate. A copy that lives on the same drive, in the same computer or in the same room as the original can be lost in the same accident.
- A second folder on the same drive is not a backup. If the drive fails, both copies go.
- {{sync|Sync}} is not a backup. A synchronised folder, such as a cloud folder that mirrors your laptop, copies changes in both directions. If you delete a file or ransomware scrambles it, the damage is copied too. Sync is convenient, but it only protects you if the service also keeps old versions or a bin.
- A backup you have never tested is a hope, not a plan. You will practise restoring in the next lesson.
- Keeps folders matching
- Delete on laptop: deleted in the cloud too
- Ransomware changes are copied across
Convenient, but it mirrors mistakes.
- Keeps copies from the past
- Delete on laptop: the backup still has it
- Restore the old good version
Protects against mistakes and loss.
Read this figure as text
A comparison of what happens to a deleted file with sync and with a backup.
Two columns. Column one, Sync: you delete Report.docx on your laptop; the cloud folder deletes it too within moments, so now both are gone, unless the service keeps a recycle bin. Verdict: sync mirrors your mistakes. Column two, Backup: you delete Report.docx on your laptop; the backup still holds yesterday's copy, so you restore it. Verdict: a backup keeps an older safe copy.
Where to keep a backup
There are three common places. Each protects against different dangers and has its own cost.
| Kind | Where it is | Strengths | Weaknesses |
|---|---|---|---|
| Local | A second internal drive or folder in the same computer | Fast, cheap | Lost with the computer to theft, fire or a power surge |
| External drive | A USB hard disk or SSD that you plug in | Large, you own it, works offline | Must be plugged in; can be lost, damaged or forgotten; keep it away from the laptop |
| Cloud | Storage online with a provider | Off-site, automatic, reachable from anywhere | Needs the internet, slow for the first large copy, monthly cost beyond free allowances, and you trust a company with your data |
The 3-2-1 idea
Professionals use a simple rule, the 3-2-1 rule. Keep 3 copies of your important data (the original and two backups), on 2 different kinds of storage (for example the laptop and an external drive), with 1 copy off-site (for example in the cloud). Each part answers a danger. Three copies mean one failure is not enough to lose everything. Two kinds of storage mean one kind of fault cannot take out both. One off-site copy survives theft and fire.
Read this figure as text
A diagram showing a laptop, an external drive and a cloud service, illustrating three copies on two kinds of storage with one off-site.
A laptop on the left holds copy one, the original, at home. An external drive in the middle, also at home, holds copy two. A cloud service on the right, outside the home zone, holds copy three. The laptop and the external drive are two kinds of storage, and the cloud is the off-site copy. Arrows run from the laptop to the drive and from the laptop to the cloud.
Version history: going back in time
Some mistakes are not noticed for days. You save over a document, and a week later you realise that a page is missing. A plain copy of the latest state cannot help. {{version-history|Version history}} keeps earlier states of a file so you can go back to an older one. Many cloud services and backup tools keep versions for a set time, such as 30 days. When you choose a backup tool, check that it keeps old versions as well as the newest.
Common mistakes
✖ Instead of: Thinking that a copy in a second folder on the same drive is a backup.
✔ Do this: Keep backups on a different device, and at least one in a different place.
✖ Instead of: Relying on sync alone.
✔ Do this: Add a real backup or check that your cloud service keeps old versions and a recycle bin.
✖ Instead of: Leaving the backup drive permanently plugged in next to the laptop.
✔ Do this: Unplug it when finished where you can, and keep a copy off-site. Ransomware can reach a connected drive.
If something goes wrong
- I deleted a file by mistake and I need it back.
- Open the Trash (Ubuntu) or Recycle Bin (Windows) first and restore it from there. If it is not there, check your cloud service's bin or version history, then your backup. Avoid saving lots of new files in the meantime.
- My backup drive is not showing up on the computer.
- Try another cable or port, check that the drive has power if it needs it, and see whether it appears in Files or File Explorer. If it makes clicking noises, stop using it and seek help.
- I am not sure how much space my backup needs.
- Open Properties on your Documents and Pictures folders to see their sizes, add them up, and choose storage at least twice that size, so that older versions fit as well.
Key terms
- Backup
- A separate copy of your files kept so you can get them back if the originals are lost or damaged.
- 3-2-1 rule
- Keep three copies of your data, on two kinds of storage, with one copy kept somewhere else.
- Version history
- A record of earlier states of a file, so that you can go back to an older one.
- Sync
- Keeping the same files up to date on more than one device or place.
Practise it for real
Reading is not the same as being able to do it. Complete these on your own computer, then tick only what you have actually done. These ticks are your own honest record: nothing checks them for you.
Audit what you could not afford to lose
On paper or in a note, list the ten files or folders on your laptop that would hurt the most to lose. Beside each, write where its copies are today: only on the laptop, on a drive, in the cloud. Then count how many items have no copy anywhere else. Do not open or move anything.
Challenge: apply 3-2-1 to a story
Wanjiru keeps her business records and 4,000 family photographs on one laptop. She keeps a copy of the photographs in a second folder on the same laptop. Write a short plan in your own words that fixes her problem using the 3-2-1 idea: which copies, on what kinds of storage and where the off-site one lives. Explain what danger each part protects against.
Knowledge check
6 questions. You need 80% to pass. Mistakes here are part of learning, and you can retry as often as you like.
Summary
- Data is lost through deletion, device failure, theft, malware, damage and software faults.
- A backup is a separate copy; a second folder on the same drive and sync alone are not enough.
- Local, external drive and cloud backups each protect against different dangers.
- The 3-2-1 idea: three copies, two kinds of storage, one off-site.
- Version history lets you return to an earlier state of a file.
Checklist: can you do these?
Marking a lesson as read does not prove you can do it. Skills count as demonstrated when you pass the quiz (not yet) and complete the practical tasks (not yet).
Related lessons
References and further reading
Official sources for details that can change between versions.
- Ubuntu Desktop guide: back up your files (Ubuntu)
- Windows support: backup and restore (Microsoft)
- CISA: back up your data (CISA)