Durable storage and restore tests

15-minute session: read for 3 minutes, trace for 3, experiment for 7, and complete the check for 2. Spend longer whenever you need.

A backup is useful only if it restores the data and required metadata. Plan consistent database and repository snapshots together. A checksum detects changed bytes; it does not prove a database is logically valid. Define a recovery-point target and recovery-time target. Practice a restore in an isolated environment before an outage.

Practice and evidence: Predict the example or draw its state transitions. Change one assumption, test the boundary, and record the actual result. Explain what this small model does not establish about a production system.

import hashlib
original=b"study record v1"
restored=bytes(original)
assert hashlib.sha256(original).digest()==hashlib.sha256(restored).digest()
print("Bytes match; application checks still needed")

Expected result: Bytes match; application checks still needed

Practice and evidence

Keep three notes: your prediction, the actual result, and why they match or differ. The completion check grades understanding; the practice task builds skill.