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Block storage cost: SAA-C03 study notes and practice questions

What to know about Block storage cost for the SAA-C03 exam, from the Design Cost-Optimized Architectures domain (20% of the exam guide), then 1 free question to test it. Part of the SAA-C03 study guide.

Last verified October 2026 against current AWS documentation ·How we write our questions

What to know for the exam

Block storage cost questions usually ask you to pick or change an EBS volume type so it costs less without falling short on performance.

EBS volume types

Type	Performance	Use for
gp3 (SSD)	3,000 IOPS and 125 MiB/s included at any size; buy more IOPS and throughput separately	The default for most workloads: boot volumes, databases, dev and test
gp2 (SSD)	3 IOPS per GiB (minimum 100), bursting to 3,000 for small volumes with burst credits	Older default; migrating to gp3 is usually cheaper
io2 Block Express (SSD)	Up to 256,000 IOPS, 99.999% durability, Multi-Attach	Critical databases needing sustained high IOPS and low latency
io1 (SSD)	Provisioned IOPS	Older provisioned IOPS type
st1 (HDD)	Throughput optimized	Large, sequential reads and writes: big data, logs, data warehouses
sc1 (HDD)	Cold, lowest cost	Infrequently accessed sequential data

HDD volumes (st1, sc1) can’t be boot volumes.

Key facts

Changing volume type is online. Elastic Volumes lets you switch gp2 to gp3, or change size, IOPS and throughput, without detaching the volume.
gp3 vs gp2: gp3 is cheaper per GB and decouples performance from size, so you don’t overprovision storage just to get IOPS.
Snapshots are incremental and stored in S3. EBS Snapshots Archive cuts storage cost by about 75% for snapshots kept 90 days or more (restores take hours). Amazon Data Lifecycle Manager or AWS Backup automate creation and deletion.
Unattached volumes and old snapshots keep billing. Trusted Advisor and Compute Optimizer find them.
Instance store is included in the instance price but is lost when the instance stops.

How to choose

“A 500 GiB gp2 volume can’t sustain 3,000 IOPS”: gp3 gives 3,000 IOPS at any size, for less.
“Database needs 50,000 IOPS consistently”: io2 Block Express.
“Large log files written and read sequentially, lowest cost”: st1.
“Keep monthly snapshots for 7 years”: snapshot archive tier.

Common traps

Growing a gp2 volume just to get more IOPS. gp3 lets you buy IOPS without buying storage.
io2 for workloads gp3 can handle. It costs much more.
HDD for boot volumes or random I/O.

Try the 1 practice question

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Question 1

Harder ·Link to this question

A company has 300 Amazon EBS gp2 volumes of 500 GiB each, attached to running EC2 instances.

Monitoring shows that each volume peaks at about 2,500 IOPS and 110 MiB/s. During long busy periods, some volumes run out of burst credits and slow down.

The company wants lower storage costs and steady performance, and the instances must stay online.

Which solution meets these requirements MOST cost-effectively?

Choose one answer.

A. Use Elastic Volumes to grow each gp2 volume to 1,000 GiB, giving a 3,000 IOPS baseline that does not depend on burst credits.
B. Use Elastic Volumes to change each volume to io2 with 3,000 provisioned IOPS, keeping the 500 GiB size.
C. Use Elastic Volumes to change each volume to gp3 with 3,000 IOPS and 125 MiB/s, keeping the 500 GiB size.
D. Snapshot each volume, create gp3 volumes from the snapshots, and swap them onto the instances during a maintenance window.

Show the answer and explanation

Answer: C

A. Wrong: gp2 gives 3 IOPS per GiB, so 1,000 GiB does provide a steady 3,000 IOPS baseline, and Elastic Volumes can grow volumes while they are in use. But doubling the storage roughly doubles the bill, which works against the goal of lowering cost. Learn more: Amazon EBS General Purpose SSD volumes (opens in a new tab)
B. Wrong: io2 Provisioned IOPS volumes give steady performance, but they are built for demanding I/O workloads and bill for every provisioned IOPS on top of storage. gp3 includes 3,000 IOPS in its storage price, so io2 would raise costs for no benefit here. Learn more: Amazon EBS pricing (opens in a new tab)
C. Right: Correct. A 500 GiB gp2 volume has a baseline of only 1,500 IOPS and relies on burst credits to reach 3,000. gp3 includes a steady 3,000 IOPS and 125 MiB/s, which covers the 2,500 IOPS and 110 MiB/s peaks, costs about 20% less per GiB, and Elastic Volumes changes the type while the volume stays in use. Learn more: Modify an Amazon EBS volume using Elastic Volumes operations (opens in a new tab)
D. Wrong: gp3 is the right volume type, but detaching and swapping volumes means taking applications offline, which the company has ruled out. Elastic Volumes can change the type of an attached volume in place, so there is no need for snapshots and a maintenance window. Learn more: Modify an Amazon EBS volume using Elastic Volumes operations (opens in a new tab)

Explanation

gp2 performance scales at 3 IOPS per GiB, so a 500 GiB volume has a 1,500 IOPS baseline and only reaches 3,000 IOPS while burst credits last. gp3 includes 3,000 IOPS and 125 MiB/s regardless of size, never relies on burst credits, and has a 20% lower price per GiB than gp2. Elastic Volumes changes the type of an attached volume while it is in use, so the instances stay online.

Study

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Amazon EBS General Purpose SSD volumes