Amazon Elastic Compute Cloud (EC2) root device volume refers to the primary block storage device that is attached to an EC2 instance and contains the operating system and other essential software. The root device volume is created automatically when an instance is launched, and it is used to store the instance’s boot volume.

The root device volume can be either an Amazon Elastic Block Store (EBS) volume or an instance store volume. An EBS volume is a network-attached block storage device that can be attached to an instance and used as a primary device for storing data. An instance store volume, on the other hand, is a temporary, disk-based storage device that is physically attached to the host computer that is running the instance.

When launching an EC2 instance, users can choose the type of root device volume they want to use. EBS volumes offer greater durability and can be detached from an instance and reattached to a different instance, making them ideal for critical applications that require high availability and data durability. Instance store volumes, on the other hand, are less expensive and can offer higher performance, but they are not durable and can only be used for temporary storage.