I came across this question and thought it is simple, my choice is A but it turns out the right answer is C.
Can anyone share me with any explain please? Thank you very much.
Which of the following approaches provides the lowest cost for Amazon Elastic Block Store snapshots while giving you the ability to fully restore data?
A. Maintain two snapshots: the original snapshot and the latest incremental snapshot
B. Maintain a volume snapshot; subsequent snapshots will overwrite one another
C. Maintain a single snapshot the latest snapshot is both Incremental and complete
D. Maintain the most current snapshot, archive the original and incremental to Amazon Glacier.
Think of an Amazon EBS Snapshot as an index to a backup of the blocks on a volume.
If a Volume has blocks 1, 2 and 3 used, then taking a snapshot will copy those three blocks to S3 and the snapshot will be an index to those three blocks.
Then, if the contents of Block 1 is changed and a Snapshot is taken, then only the updated block 1 will be copied to S3. The second Snapshot will point to the new Block 1 and the old Blocks 2 & 3. The old Block 1 will still be maintained in S3 because the first Snapshot is still using it. If the first Snapshot is deleted, then the old Block 1 will be discarded.
That is why the lowest-cost option is to maintain only the latest Snapshot, since it contains the smallest about of backed-up blocks.
Snapshots are incremental in that they backup whatever has not been previously backed-up by another (existing) snapshot.
Update: See: AWS re:Invent video that explains the 'incremental' concept of Amazon EBS volumes