Jeff’s Note #
Unlike generic exam dumps, ADH analyzes this scenario through the lens of a Real-World Site Reliability Engineer (SRE).
For SOA-C02 candidates, the confusion often lies in how AWS Backup snapshots leverage incremental storage yet require precise calculation of total snapshot size.
In production, this is about understanding exactly how changed blocks affect backup costs and storage overhead. Let’s drill down.
The Certification Drill (Simulated Question) #
Scenario #
You are a Site Reliability Engineer at FinData Solutions, a fintech startup responsible for managing backups of critical workloads. The team uses AWS Backup to automatically capture snapshots of a single Amazon EC2 instance’s attached Amazon EBS volume.
The EBS volume holds persistent data that changes over time:
- For the first snapshot, the volume contains 10 GiB of data.
- For the second snapshot, the volume size remains 10 GiB, but 4 GiB of the data blocks have changed since the first snapshot.
- For the third snapshot, the volume grew to 12 GiB, meaning an additional 2 GiB of data has been added since the second snapshot.
The Requirement: #
Determine the total amount of storage consumed by all three incremental snapshots combined.
The Options #
- A) 12 GiB
- B) 16 GiB
- C) 26 GiB
- D) 32 GiB
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leave a comment:
Correct Answer #
B) 16 GiB
Quick Insight: The SysOps Imperative #
AWS EBS snapshots are incremental, meaning only changed blocks after the initial snapshot consume additional storage.
The total storage used is the size of the first full snapshot plus all unique changed blocks captured in subsequent snapshots.
This is key to accurate backup storage calculations and cost forecasting.
Content Locked: The Expert Analysis #
You’ve identified the answer. But do you know the implementation details that separate a Junior from a Senior?
The Expert’s Analysis #
Correct Answer #
Option B) 16 GiB
The Winning Logic #
AWS EBS snapshots are inherently incremental after the first snapshot:
- The first snapshot stores the entire 10 GiB volume.
- The second snapshot records only the data blocks that changed since the first snapshot. Since 4 GiB are changed, those 4 GiB are new storage.
- The third snapshot adds 2 GiB of new data compared to the second snapshot, so 2 GiB additional storage is required.
Total storage = 10 GiB (initial) + 4 GiB (second snapshot changes) + 2 GiB (third snapshot changes) = 16 GiB.
This matches how AWS Backup and EBS snapshots handle incremental block storage.
The Trap (Distractor Analysis): #
- Why not A) 12 GiB? Assumes only final size of volume matters, ignoring the incremental nature of changed blocks across snapshots.
- Why not C) 26 GiB? Incorrectly sums total sizes of snapshots rather than just the changed data blocks after the first snapshot.
- Why not D) 32 GiB? Double counts data changes or incorrectly assumes snapshots store full volumes each time, which is not true for EBS snapshots.
The Technical Blueprint #
# To check the sizes of snapshots associated with a volume, use:
aws ec2 describe-snapshots --filters Name=volume-id,Values=vol-xxxxxxxx
# Snapshot storage is incremental:
# Initial snapshot stores full data,
# subsequent snapshots only store changed blocks,
# leading to cost-efficient backup storage.
The Comparative Analysis (SysOps Focus) #
| Option | Operational Overhead | Automation Level | Impact on Storage Cost |
|---|---|---|---|
| A) 12GiB | Underestimates storage | Simplifies calculation but inaccurate | Could lead to under-budgeting costs |
| B) 16GiB | Correct calculation | Reflects real incremental snapshot behavior | Accurate cost and storage forecasting |
| C) 26GiB | Overestimates changed data | Overcomplex, misinterprets snapshot logic | Leads to inefficient budgeting |
| D) 32GiB | Assumes full snapshot each time | Ignores incremental tech | Highest cost estimate, unrealistic |
Real-World Application (Practitioner Insight) #
Exam Rule #
“For SOA-C02 exams, always remember: EBS snapshots are incremental after the initial snapshot; only changed blocks consume additional storage.”
Real World #
“In real environments, understanding this helps optimize backup windows, storage costs, and recovery workflows. Many overlook that snapshot size grows proportional to changed blocks, not total volume size.”
(CTA) Stop Guessing, Start Mastering #
Disclaimer
This is a study note based on simulated scenarios for the SOA-C02 exam.