Backup means making a copy of data and storing it separately. Recovery means using that copy to restore the data after loss or damage. Questions usually ask you to explain why each matters, or to compare two backup methods.
This lesson belongs to safety, security and effects and follows on from data-protection risks, where loss is one of the dangers.
What are the common backup types?
A full backup copies everything. It is simple to restore but takes the most time and storage.
An incremental backup copies only what changed since the last backup of any kind. It is quick and small, but recovery needs the last full copy plus every incremental in order.
A differential backup copies what changed since the last full backup. Recovery needs the full copy plus only the latest differential.
Worked example
Invented case: Lotus Print Shop (fictional) makes a full backup of 80 GB every Sunday night. From Monday to Thursday it makes an incremental backup of 4 GB each night. The computer fails on Friday morning.
Step 1, what exists? One full backup (Sunday) and four incrementals (Monday, Tuesday, Wednesday, Thursday).
Step 2, what is needed to recover? The full backup and all four incrementals, restored in date order.
Step 3, total data restored: 80 + (4 × 4) = 80 + 16 = 96 GB.
Step 4, check: four nights at 4 GB is 16 GB, and 80 + 16 = 96. Correct.
If the shop had used differential backups, recovery would need only the Sunday full copy and Thursday’s differential, which holds all the changes since Sunday. The trade-off is that each differential grows larger during the week.
The mistake to watch for
A common slip is describing backup as the way to get data back.
Mistaken answer: “Backup is when you restore your files after the computer breaks.”
That describes recovery. A backup is the copy made earlier.
The correction is to use two separate sentences: “A backup is a copy kept separately. Recovery is using that copy to restore the files.” Another slip is storing the backup on the same computer, which fails if that computer is lost.
Check yourself
1. Give one reason a school should keep a backup copy off the premises.
Show answer
A fire, flood or theft at the school could destroy both the original data and an on-site copy. An off-site copy survives the event.
2. A business makes a full backup of 60 GB on Sunday and incrementals of 3 GB on each of Monday, Tuesday and Wednesday. The system fails on Thursday. How much data is restored?
Show answer
60 + (3 × 3) = 60 + 9 = 69 GB, restoring the full backup and then the three incrementals in order.
3. Why should you test a restore, not only make backups?
Show answer
A backup that cannot be restored is no use. Testing shows whether the files open correctly before a real failure happens.
Where this leads next
Continue to comparing authentication controls, then return to the practice set. The mistake log is a good place to record any term you mixed up.
Students who understand each term but blur them under timed conditions can work through examples in online one-to-one ICT tuition.