EBS is a network-attached storage volume for your EC2 instance. Think of it as an external hard drive that connects over the network — it is not a physical drive plugged directly into the server.
Because it connects over the network, you can detach it from one instance and attach it to another, just like unplugging a USB drive and moving it to a different computer.
An EBS volume is created in a specific AZ and can only be attached to instances in that same AZ. A volume in us-east-1a cannot be directly attached to an instance in us-east-1b.
To move data across AZs, you need to take a snapshot first.
By default, one EBS volume can only be attached to one EC2 instance at a time — similar to how a USB stick works with one computer at a time.
Exception: io1 and io2 volume types support Multi-Attach, allowing the same volume to be attached to multiple instances simultaneously within the same AZ.
When an EC2 instance is terminated, the attached EBS volume is not automatically deleted by default (except the root volume — see below). Your data persists and the volume can be attached to a new instance.
When launching an EC2 instance, each EBS volume has a "Delete on Termination" option:
For the root volume, this is enabled by default. For additional data volumes, it is disabled by default.
If you store important data on the root volume, disable this setting to prevent accidental data loss when an instance is terminated.