LearnGlossary

What is block storage?

Updated 25 October 2026 · Published by Zoorik

Block storage is storage that a server uses as a disk. You pick its size and attach it to a cloud virtual machine (VM). It works like a local hard drive.

Block storage in AWS and Azure

Block storage in cloud computing is a disk you rent: Amazon Elastic Block Store (EBS) volumes on AWS, managed disks on Azure.

Each Azure VM has these disks:

  • One operating system disk (OS disk), which the VM starts from.
  • Data disks you add, for your apps and data.
  • On most VMs, a temporary disk, which isn’t a managed disk and can lose data.

Block storage vs object storage

Object storage, such as Amazon S3, stores each file and its metadata as an object in a bucket. Apps fetch an object by its key, its unique name in the bucket, through a web API.

Bills differ too. A disk bills for the size you provision, full or not. Amazon S3 charges only for what you actually use.

A disk bills the size you provision. Amazon S3 bills only what you use. Illustration, with no measurements. Two rows. Block storage, Amazon EBS volumes on AWS and managed disks on Azure: a VM box with an arrow labelled attached, works like a local hard drive, to a Disk box. Inside the disk, a bar holds Data and an amber span labelled Empty, still billed. A bracket under the whole bar reads Billed: the size you provision. Object storage, such as Amazon S3: an App box with an arrow labelled fetches objects by key, through a web API, to a Bucket box that holds three objects, labelled Objects (file + metadata). A bracket under the objects only reads Billed (Amazon S3): what you actually use. A disk bills the size you provision. Amazon S3 bills only what you use. Block storageAmazon EBS volumes on AWS, managed disks on AzureVMattached, works like a local hard driveDiskDataEmpty, still billedBilled: the size you provisionObject storagesuch as Amazon S3Appfetches objects by key, through a web APIBucketObjects (file + metadata)Billed (Amazon S3): what you actually use
Illustration, no measurements: a disk is billed for its whole provisioned size, empty space included, while Amazon S3 charges only for the objects it stores.

Why it matters for your bill

Microsoft’s billing example is a 1 TiB Standard SSD (solid-state drive) holding 120 GiB of data. You pay for all 1 TiB.

  • Sizing a disk to its data, called rightsizing, can reduce that cost.
  • Amoeba moves a VM’s data disks onto one pool sized to your data, then rightsizes it autonomously. It never touches the OS disk or root volume.
  • It works on Azure managed disks and Amazon EBS volumes, on Windows and Linux VMs.
  • The free assessment works out your own figure.
  • For Azure disks, read Azure disk cost optimization.

Read next: Azure disk cost optimization

Sources: Amazon Web Services, “What is Amazon Elastic Block Store?” (opens in a new tab); Microsoft Learn, “Overview of Azure Disk Storage” (opens in a new tab); Microsoft Learn, “Understand Azure Disk Storage billing” (opens in a new tab); Amazon Web Services, “What is Amazon S3?” (opens in a new tab).

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