What is block storage?
In our journey through cloud security—from Encryption at Rest to Vulnerability Management—we’ve spent a lot of time talking about how to protect data. But where does that data actually live?
The foundation of high-performance cloud computing is Block Storage. If you’ve ever added a "hard drive" to a Virtual Machine, you’ve used Block Storage.
In the cloud, data storage is generally split into three types: File, Object, and Block.
Block Storage is the most basic. It takes a massive storage volume and chops it into small, equal-sized "blocks." Each block has a unique address but no metadata (no file name, no creation date, no owner).
The Analogy: Think of a Parking Garage.
The data is the car.
The "Block" is the parking space.
The system doesn't care if the car is a Ferrari or a Ford; it just knows that "Car A" is in "Space 402." This makes it incredibly fast to retrieve and move cars because the system doesn't have to navigate a complex "map" of folders.
Because block storage is "raw," it provides the fastest possible way for a server to read and write data. This is why it is the default choice for Databases (like SQL or Oracle) and Operating Systems.
To your Virtual Machine (EC2, Azure VM), a block storage volume looks like a blank, unformatted physical hard drive. You can format it with any "File System" you want (like NTFS for Windows or Ext4 for Linux).
In a physical data center, if you ran out of disk space, you had to buy a new drive and physically plug it in. In the cloud, you can "expand" a block storage volume with a single click while the server is still running.
This is the most common point of confusion in the cloud. Here is the breakdown:
| Feature | Block Storage (e.g., AWS EBS) | Object Storage (e.g., AWS S3) |
| Structure | Raw blocks of data. | Data + Metadata + Unique ID. |
| Speed | Very Fast (Low Latency). | Slower (High Throughput). |
| Use Case | Databases, Boot Disks. | Photos, Videos, Backups. |
| Access | Must be attached to a server. | Accessible via Web URL/API. |
| Cost | More expensive. | Very cheap. |
One of the best features of block storage is the Snapshot. You can take a "point-in-time" copy of your entire disk. If your server is hit by ransomware or a bad code update, you can "rewind" the disk to the state it was in yesterday in minutes.
As we discussed in our [Encryption post], most cloud providers (AWS, Azure, Google) now allow you to encrypt block storage volumes with one click. The performance "hit" for doing this is virtually zero, making unencrypted disks a major red flag in 2026.
Persistent: The data stays there even if you turn off or delete the Virtual Machine.
Ephemeral (Instance Store): The data is physically attached to the server host. It is insanely fast, but if the server stops, the data is deleted forever. Never put your primary database on ephemeral storage!
AWS: Elastic Block Store (EBS)
Azure: Azure Managed Disks
Google Cloud: Persistent Disk
Open Source: Ceph or OpenStack Cinder
Block Storage is the "muscle" of cloud storage. It’s built for speed, reliability, and high-performance workloads. While it isn't as "smart" as Object Storage, it is the essential foundation that allows your databases and applications to run at the speed of modern business.