Thin-Provisioned EBS Volumes: Pay Only for What You Use (And When You Shouldn’t)

Managing storage costs on AWS can feel like juggling fire—one misstep, and you’re burned by high fees. That’s where thin-provisioned EBS volumes can help, offering a way to avoid paying for large, fully-provisioned volumes when you’re barely using a fraction of the storage. With thin provisioning, you only pay for the data you actually use while still having the capacity to scale up when needed.

This article assumes you’ve got EC2 or EKS set up and are looking for ways to optimize your storage costs. We’ll dive into how thin provisioning works, when it shines, when to avoid it, and how to set it up—especially in Kubernetes on EKS.

What Is Thin Provisioning?

Thin provisioning is like smart budgeting for your cloud storage. Instead of paying for a full storage volume up front—even if you’re not using it—you only pay for the actual data you store. This concept is especially useful for environments where you need flexibility in scaling storage but don’t want to overpay for empty space.

Let’s say you provision a 1TB EBS volume for your application, but your app is only storing 100GB of data. With thin provisioning, AWS only charges you for the 100GB that you’re actually using, not the full 1TB. It’s like renting a massive warehouse but only paying for the portion of shelves you’re actively filling. As your data grows, your costs gradually increase, but you’re always in control of how much space you need.

How Thin Provisioning Works

In AWS, when you create an EBS volume, you can define a larger volume size—say, 1TB—but thanks to thin provisioning, you only pay for the actual data written to the volume. For example, if your app only uses 50GB out of the 1TB, you’re only charged for those 50GB. Over time, as your data grows, the amount you’re billed for increases, but only based on the data you’re actively storing.

However, thin provisioning doesn’t automatically expand the volume if you fill up that initial 1TB. Here’s where the key clarification comes in:

• Within the provisioned limit: Thin provisioning means you only pay for the data you use. As your data grows, you’re still working within the provisioned size (e.g., 1TB), and costs adjust dynamically based on usage. You don’t need to worry about manual resizing while your data is still within that limit.
• When the volume reaches its limit: Once your stored data hits the 1TB limit of your thin-provisioned volume, AWS will not automatically increase the size of the volume. This is the important part—thin provisioning optimizes your cost, but if you need more space than you initially provisioned, you have to either manually or automatically resize the volume to expand beyond that 1TB.

Without additional steps, your app could run into storage issues once it hits the ceiling of the volume’s provisioned size. To prevent this, you can automate the process of expanding the volume when it gets close to full capacity. This would require a custom lambda function or similar solution (potentially a Kubernetes operator for EKS).

When to Use Thin-Provisioned EBS Volumes

1. Low Utilization, Flexible Growth

For environments where you don’t need a lot of storage upfront—like development or testing environments—thin provisioning is a great option. You create a large volume without paying for all of it, but if your data grows, the volume expands, and costs adjust accordingly. It’s the perfect mix of flexibility and cost-efficiency.

Example: If you provision a 1TB volume but only use 50GB, you’ll only be paying for 50GB, not the full 1TB. As your data grows, your costs will increase in line with your storage usage.

2. Slow, Predictable Data Growth

If your application’s data grows slowly, thin provisioning can help you avoid paying for large volumes until you actually need them. This is common with applications that store logs, backups, or archival data, where storage grows over time but not rapidly.

Example: Let’s say your app logs 1GB of data per day. Rather than provision a massive volume upfront, you can start small, paying for only what you use and allowing the volume to grow as the logs accumulate.

3. Avoiding Overprovisioning

How many times have you over-provisioned storage “just in case” and ended up paying for empty space? Thin provisioning stops that waste. You get the volume size you think you’ll need but don’t pay for it until it’s used.

When NOT to Use Thin-Provisioned EBS Volumes

1. High-Performance Applications

If your application requires a lot of input/output operations (I/O)—like a production database—you might want to stick with full provisioning. Thin provisioning is fine for apps that don’t need high performance all the time, but for heavy workloads, fully provisioning the volume ensures that your storage can keep up with your app’s demands.

Example: If your app constantly reads and writes to a database and relies on consistent, high IOPS (Input/Output Operations Per Second), full provisioning will ensure there’s no risk of performance bottlenecks.

2. Rapid, Unpredictable Data Growth

If you expect your data to explode overnight—think user-generated content like videos or social media uploads—thin provisioning could hit you with unexpected cost spikes. Fully provisioning in these cases locks in the cost and avoids surprises.

Example: Launching a new social media app where you expect a rapid influx of data. Thin provisioning might not be ideal if data usage grows unpredictably because it can result in unexpected bills as your storage suddenly balloons.

3. Consistently High Utilization

If you know from the start that your volume will be full, thin provisioning doesn’t make much sense. You’re better off fully provisioning to avoid the extra management overhead.

Example: Running a video processing app that requires large amounts of space right from the get-go. In this case, fully provisioning will save time and effort since you know you’ll be using the entire volume right away.

Cost Example: Thin Provisioning vs. Fully Provisioned EBS Volumes

Let’s break it down with a real example:

Fully Provisioned Volume:

You provision a 1TB volume with standard gp2 (general-purpose SSD) storage. AWS charges $0.10/GB per month, meaning you’ll pay:

• 1TB (1,000GB) × $0.10 = $100/month.

That’s $100/month, even if you’re only using a tiny fraction of that space.

Thin Provisioned Volume:

Now, let’s thin provision that same 1TB volume, but you’re only storing 100GB of actual data. In this case, AWS only charges for the 100GB of used space:

• 100GB × $0.10 = $10/month.

So, instead of paying $100/month, you’re only paying $10—a significant difference, especially when scaled across multiple volumes.

This is why thin provisioning is a game changer for low-utilization workloads. As your data grows, your costs will scale, but you’re avoiding upfront overpayment for unused storage.

Setting Up Thin-Provisioned EBS Volumes in Kubernetes/EKS

In Kubernetes, storage is handled via StorageClasses, and to set up thin provisioning for EBS volumes in EKS, the critical setting you need is allowVolumeExpansion: true. This allows the volume to expand dynamically as your app needs more storage.

Here’s a quick example of a StorageClass with thin provisioning in Kubernetes:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: ebs-thin-provisioned
provisioner: ebs.csi.aws.com
parameters:
  type: gp3               # General Purpose SSD (gp3) is cost-effective and performant
  fsType: ext4            # Filesystem type
  csi.storage.k8s.io/fstype: ext4
  encrypted: "false"      # Set to "true" if you require encryption
  iopsPerGB: "3"          # Optional: Customize IOPS based on your workload
  throughput: "125"       # Optional: Customize throughput based on your workload
reclaimPolicy: Delete     # Determines what happens to the volume when the PVC is deleted
allowVolumeExpansion: true # Allows the volume to be resized after creation
volumeBindingMode: WaitForFirstConsumer # Binds the volume to the node when a Pod is scheduled

The key setting here is allowVolumeExpansion: true, which tells Kubernetes to allow the volume to grow as your storage needs increase.

Once the StorageClass is in place, you can create a PersistentVolumeClaim (PVC) to request storage dynamically. Here’s a simple example:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: thin-provisioned-pvc
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: ebs-thin-provisioned
  resources:
    requests:
      storage: 50Gi # Requested storage is 50GB, but you'll only pay for what's used

With this setup, if you request 50GB of storage but only use 10GB, you’re only paying for 10GB.

Final Thoughts: Should You Go Thin or Full?

Thin provisioning is ideal for low-utilization or slow-growing environments, offering flexibility without overpaying upfront. It’s especially useful in development and testing environments where the full storage might not be needed immediately.

But, if you’re running high-performance apps or expecting rapid data growth, fully provisioned volumes might be the better call to ensure consistent performance and predictable costs.

When set up properly, thin provisioning in Kubernetes/EKS can help you save on storage costs while keeping your infrastructure scalable and flexible. Just make sure to monitor usage, automate where possible, and consider the specific needs of your workloads before choosing between thin or full provisioning.