← VCE Software Development U3O2

Incremental backup

A backup that copies only files changed since the last backup of any type. It is small and fast, but a restore needs the full backup plus every increment.

Part of: VCE Software Development - U3O2 - Analysis and Design — Module 78, VCE Data Analytics - U3O2 - Analysis and Design — Module 115, VCE Data Analytics - U4O2 - Cyber Security: Data Security — Module 83

Understanding Incremental backup in VCE Software Development U3O2

What it does: After the large full backup, each incremental is only a few GB because it holds just the recent changes, so it runs quickly. Increments depend on each other, so a damaged one can break the restore chain. They are not complete copies. A restore needs the full backup plus every increment in order, so no link in the chain can be missing.

Common mistakes: An incremental backup copies only the files that changed since the last backup. Copying every file again would be a full backup. It should be 'Mon: changes since Sun'. An incremental backup compares files with the last backup of any type, which was Tuesday's. Comparing with Sunday's full backup describes a differential backup. It should be 'Wed: changes since Tue'.

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This module's key terms are also in a printable crossword (Modules 72–85) and word search (Modules 52–85).

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Learning
Duo
An incremental backup copies only the files changed since...
the last full backup onlythe last backup of any type (full or incremental)
Matches
Wed Inc copies everything changed since Monday's Full backup
↓
This describes a differential backup. An incremental backup only copies changes since the last backup of any type, which here is Tuesday's incremental.
Applying
Meanings
Term
incremental backup
Meaning
A backup that copies only files changed since the last backup of any type. It is small and fast, but a restore needs the full backup plus every increment.
Practice
BEGIN IncrementalBackup
Testing
Gaps
backupType ←
Check Answer
Spots
1Sun: full backup
2Mon: copy every file again

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Quick Questions

1. An incremental backup copies only the files changed since...
A. the last backup of any type (full or incremental) ✓
B. the last full backup only
Incremental compares against the most recent backup of any type. Comparing against the last full backup is a differential backup.
2. Compared with a full backup, an incremental backup is usually...
A. smaller and faster to run ✓
B. larger and slower to run
Because it copies only recently changed files, an incremental backup uses less storage and takes less time.
3. On Monday you take a full backup. On Tuesday you take an incremental backup. What does the Tuesday backup contain?
A. Only the files changed since Monday's full backup ✓
B. Every file on the system
Tuesday's incremental copies only the changes made since Monday. Copying every file would be a full backup.
4. On Wednesday you take another incremental backup. Which files does it copy?
A. Files changed since Monday's full backup
B. Files changed since Tuesday's incremental backup ✓
Each incremental is measured against the previous backup of any type, so Wednesday only covers changes since Tuesday.
5. To restore data from incremental backups, you need...
A. only the most recent incremental backup
B. the full backup plus every incremental backup since it ✓
Each increment holds only a slice of the changes, so the restore needs the full backup and every increment in order.

Match the Pairs

incremental backup → Copies only the files changed since the last backup of any type (full or incremental)
Full + Inc1 + Inc2 + Inc3 → The set of backups needed to restore data after the third incremental backup
Small and fast: each incremental backup only copies files changed since the last backup of any type → Mon: Full 50 GB | Tue: Inc 1 GB | Wed: Inc 2 GB
Restore needs the full backup plus every increment, applied in order → restore(Full, Inc1, Inc2, Inc3)
Wed Inc copies everything changed since Monday's Full backup → This describes a differential backup. An incremental backup only copies changes since the last backup of any type, which here is Tuesday's incremental.
Restore Thursday using the Full backup + Wed Inc only → Restoring needs the full backup plus every increment since it (Tue, Wed, Thu). Skipping increments means changes are missing.

Key Term

incremental backup
A backup that copies only files changed since the last backup of any type. It is small and fast, but a restore needs the full backup plus every increment.

Fill in the Blanks

1. backupType ← incremental
Hint: Type the name of the backup type that copies only files changed since the last backup of any type.
2. incrementalSize ← small
Hint: Type the word describing how big this type of backup is compared with a full backup.
3. restore ← fullBackup + allIncrements
Hint: Type the starting backup that must be restored first, before any increments are added.
4. Mon: full backup Tue: incremental, changes since Mon Wed: incremental, changes since Tue
Hint: Type the day of the most recent earlier backup, because an incremental compares to the last backup of any type.
5. FOR inc IN incrementsInOrder apply(inc)
Hint: Type the action name that restores each increment in the chain, one after another.

Spot the Error

Question 1
A Sun: full backup
B Mon: copy every file again
C Tue: changes since Mon
Line B — An incremental backup copies only the files that changed since the last backup. Copying every file again would be a full backup. It should be 'Mon: changes since Sun'.
Question 2
A Sun: full backup
B Mon: changes since Sun
C Tue: changes since Mon
D Wed: changes since Sun
Line D — An incremental backup compares files with the last backup of any type, which was Tuesday's. Comparing with Sunday's full backup describes a differential backup. It should be 'Wed: changes since Tue'.
Question 3
A Disk fails on Thursday
B Restore the full backup first
C Then restore only the last one
Line C — Each increment holds only a slice of the changes, so a restore needs the full backup plus every increment in order. It should be 'Then restore every increment'.
Question 4
A Incremental: large and slow
B Copies files changed since the
C last backup of any type
Line A — Because an incremental backup copies only recently changed files, it is small and fast, not large and slow.
Question 5
A IF changed since last full
B copy file to backup
C ELSE skip the file
Line A — An incremental backup checks for changes since the last backup of any type, not just the last full backup. The condition should be 'IF changed since last backup'.

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