Differential backup

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. A differential backup copies files changed since which point?

A The previous backup of any type

B The last full backup

2. Full backup on Sunday. A differential is taken Monday, Tuesday and Wednesday. Which differential is the largest?

A Monday's, because it was taken first

B Wednesday's, because it holds all changes since Sunday

3. To restore on Thursday after a Sunday full backup and daily differentials, which files do you need?

A The Sunday full backup plus Wednesday's differential

B The Sunday full backup plus the Monday, Tuesday and Wednesday differentials

4. True or false: a differential backup grows larger each day until the next full backup.

A True

B False

5. Which statement describes a differential backup?

A It copies all files changed since the last full backup

B It copies only files changed since the last differential backup

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1differential backup		AA differential backup compares to the last full backup, not the previous differential. That describes an incremental backup.
2Full + Differential (Fri)		Brestore = Full (Sun) + Differential (Wed)
3A differential backup grows each day because it keeps including earlier changes as well as new ones		CThe two backups needed to restore the system when using a differential backup strategy
4To restore from differential backups you only need the full backup and the latest differential		DFull: 10 GB, Mon: 1 GB, Tue: 2 GB, Wed: 3 GB
5Restore = Full + Mon + Tue + Wed differentials		ERestoring with every differential is wrong. Only the latest differential is needed because it contains all earlier changes.
6Tue differential = files changed since Mon differential		FCopies every file that has changed since the last full backup, not since the last differential

Definitions

differential backup

Fill in the Blanks

Complete each line of code by filling in the missing parts.

IF file.modified > lastFull THEN ____ file TO backup END IF

IF file.modified > ________ THEN COPY file TO backup END IF

RESTORE(fullBackup, __________)

diffSize ← diffSize _ todaysChanges

RESTORE(__________, latestDiff)

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A Sun: incremental backup only

B Mon: copy changes since Sun

C Tue: copy changes since Sun

Question 2

A Full backup on Sunday

B Mon diff: 2 GB

C Tue diff: 1 GB

Question 3

A restore = full + every diff

B 1: restore the full backup

C 2: restore the latest diff

Question 4

A IF day = Sunday THEN

B run DIFFERENTIAL backup

C ELSE

D run DIFFERENTIAL backup

E END IF

Question 5

A Sun: full backup

B Mon-Wed: differentials

C Thu: server crashes

D restore full + Mon diff

Answer Key

Differential backup

Section A: Quick Questions

B — The last full backup

B — Wednesday's, because it holds all changes since Sunday

A — The Sunday full backup plus Wednesday's differential

A — True

A — It copies all files changed since the last full backup

Section B: Match the Pairs

differential backup → Copies every file that has changed since the last full backup, not since the last differential

Full + Differential (Fri) → The two backups needed to restore the system when using a differential backup strategy

A differential backup grows each day because it keeps including earlier changes as well as new ones → Full: 10 GB, Mon: 1 GB, Tue: 2 GB, Wed: 3 GB

To restore from differential backups you only need the full backup and the latest differential → restore = Full (Sun) + Differential (Wed)

Restore = Full + Mon + Tue + Wed differentials → Restoring with every differential is wrong. Only the latest differential is needed because it contains all earlier changes.

Tue differential = files changed since Mon differential → A differential backup compares to the last full backup, not the previous differential. That describes an incremental backup.

Section C: Definitions

differential backup — Copies all files changed since the last full backup. It grows each day, and a restore needs the full backup plus only the latest differential.

Section D: Fill in the Blanks

IF file.modified > lastFull THEN
  COPY file TO backup
END IF

IF file.modified > lastFull THEN
  COPY file TO backup
END IF

RESTORE(fullBackup, latestDiff)

diffSize ← diffSize + todaysChanges

RESTORE(fullBackup, latestDiff)

Section E: Spot the Error

A — A differential backup needs a full backup of all files as its starting point. Line 1 should be 'Sun: full backup of all files'.

C — A differential backup grows each day because it keeps every change since the full backup. Tuesday's backup cannot be smaller than Monday's, so it should be 3 GB.

A — Each differential already contains all changes since the full backup. A restore needs only the full backup plus the latest differential, not every one.

B — A differential backup must be based on a full backup. The full backup is made on Sunday, so line 2 should be ' run FULL backup'.

D — The latest differential (Wednesday's) holds all changes since the full backup. Using Monday's would lose the Tuesday and Wednesday changes.