When migrating a production database to Amazon RDS, understanding how AWS allocates IOPS can mean the difference between a cost-optimized design and overspending on unused capacity. While both gp2 and gp3 storage types might meet performance requirements on paper, the way they handle IOPS and capacity is fundamentally different. In this breakdown, we’ll explore the gp2 limitation, why gp3 often delivers better value, real-world analogies to make the concept stick, and AWS exam insights to help you choose the right option in both professional scenarios and certification questions.
Use Case: When You Need Speed Without Wasting Space
An engineering team is migrating its production database to Amazon RDS.
They need:
50 GiB of storage
1,000 IOPS for consistent performance
On paper, both gp2 and gp3 could work. But knowing how AWS allocates IOPS can be the difference between a cost-optimized setup and paying for storage you’ll never use.
The gp2 Limitation
With General Purpose SSD (gp2)
IOPS = 3 × GiB of allocated storage
The only way to increase IOPS is to increase the storage size.
For 1,000 IOPS:
1,000 ÷ 3 = ~334 GiB required
Even if you only actually need 50 GiB for your data.
That’s nearly 284 GiB of wasted capacity just to meet performance needs.
Analogy: Buying a Bigger Water Tank Just to Get a Faster Faucet
Imagine setting up a water system:
You only need a 50-gallon tank to store the water you’ll actually use.
But the store says, “The bigger your tank, the faster your faucet will pour.”
If you want a fast flow rate (high IOPS), you have to buy a 500-gallon tank.
The problem?
You’re paying for 450 gallons of unused space just so the water pours faster.
That’s gp2: capacity and speed are linked.
With gp3, you
Keep your 50-gallon tank (exact storage you need)
Upgrade your faucet speed (IOPS) independently — no waste, no overspending.
The gp3 Advantage
With General Purpose SSD (gp3)
Storage size and IOPS are independent.
You can provision 50 GiB and still get 1,000 IOPS without upsizing the volume.
gp3 includes 3,000 baseline IOPS at no extra cost.
Cost Comparison: gp2 vs gp3 for 1,000 IOPS
(Assuming $0.10/GB-month for gp2 and $0.08/GB-month for gp3)
gp2: $33.40/month (334 GiB)
gp3: $4.00/month (50 GiB)
When gp2 Might Still Be the Right Choice
While gp3 is generally the better fit, gp2 can still be suitable for small volumes that benefit from burst IOPS. For example, gp2 volumes under 1 TiB can burst to 3,000 IOPS temporarily, even if their baseline is much lower. This can be cost-effective for workloads with low average I/O needs but occasional short spikes in activity.
Cheat Sheet: gp2 vs gp3 – AWS General Purpose SSD Storage
Feature | gp2 | gp3 |
|---|---|---|
IOPS Allocation | 3 IOPS per GiB (capacity & IOPS linked) | IOPS set independently from capacity |
Baseline IOPS | Depends on volume size (max 16,000) | 3,000 included at no extra cost |
Scaling IOPS | Increase storage size to get more IOPS | Increase IOPS directly (up to 16,000) without adding storage |
Cost Model | Pay for total provisioned GB | Pay for GB + additional IOPS beyond the included baseline |
Example – 1,000 IOPS Need | 334 GiB @ $0.10/GB ≈ $33.40/month | 50 GiB @ $0.08/GB ≈ $4.00/month |
Best For | Legacy workloads or small volumes benefiting from burst IOPS | Most workloads needing predictable performance without over-provisioning |
Exam Tip | If scenario ties performance to size → gp2 | If the scenario needs flexible IOPS & cost optimization → gp3 |
AWS Certification Exam Insights
gp2: Ties IOPS to volume size → risk of paying for unused capacity.
gp3: Decouples storage and IOPS → flexible and cost-optimized.
In SAA-C03 questions, watch for clues like “minimum storage size,” “IOPS requirement,” and “cost-effective” — these often point to gp3.
Key Takeaways
If you see “IOPS tied to storage size” → think gp2.
If you need high performance without extra capacity → choose gp3.
Cost optimization in AWS is about matching capacity to actual needs, not just picking the lowest per-GB price.
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