ITPEC IP October 2025 Question 19
There is a system where a full backup is made after closing time every Sunday, and an incremental backup is made after closing time on Monday through Saturday. On a Wednesday, a failure happened during business hours, so a decision was made to restore data to the state at the closing time on Tuesday by using backup files. Which of the following lists all and only the necessary backup files for restoring data? Here, an incremental backup file means a backup file that contains only the data that has been modified since the previous backup (a full backup or an incremental backup) was made.
Explanation
Sunday's full backup plus Monday's and Tuesday's incremental backups — an incremental restore needs the whole chain since the last full backup.
- •Sunday full backup: every file as of Sunday closing, the base
- •Monday incremental: only what changed since Sunday's backup
- •Tuesday incremental: only what changed since Monday's backup
Restore the full backup first, then apply Monday's and Tuesday's files in that order to reach the state at Tuesday closing.
Answer (a)
Why not others:
- •(b) — skips Monday: Tuesday's file holds only the changes since Monday's backup, so Monday's changes would be lost
- •(c) — no base: incremental files hold only changed data, so files unchanged since Sunday could not be restored
- •(d) — lacks both the base and Monday's changes
Key rule: Incremental backup restores as full + every incremental in order (quick to back up, slow to restore); differential backup restores as full + only the latest differential.
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