Backups
Full, incremental and differential backups, the chain to restore, the 3-2-1 rule, acceptable data loss and downtime, retention, an offline copy against ransomware and the restore test.
- 28 cards
- 5 topics
- Free
The outline, topic by topic
Each topic is weighted the way the exam weighs it.
- Concepts
- Questions
- Sort and link
- The numbers
- Scenarios
A few cards from the deck
Full backup: what is it?
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A copy of all the chosen data, whatever the date of its last change.
It restores on its own, so quickly, but it is the slowest to make and the heaviest to store: it is made rarely.
Full backup on Sunday evening, differential every evening of the week. The disk fails on Thursday at noon. How many sets must be restored?
- 2: the full one, then Wednesday's differential
- 4: the full one, then Monday, Tuesday and Wednesday
- 1: Wednesday's differential is enough
- 3: the full one, Tuesday and Wednesday
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2: the full one, then Wednesday's differential
Each differential holds everything changed since the full backup: the latest replaces the earlier ones. Without the full one it lacks the unchanged files.
… is how long each backup is kept before being deleted; a … reuses the oldest media.
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Retention is how long each backup is kept before being deleted; a rotation reuses the oldest media.
Too short a retention lets a silently corrupted file overwrite every good copy before anyone notices.
Incremental backup: what is it?
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A copy of only the files created or changed since the previous backup, whether full or incremental.
It is the lightest and fastest to make, but restoring needs the whole chain: if one link is missing, the later sets no longer rebuild a consistent state.