What is a boot volume in reference to Amazon Web Services?

Question

What is a 'boot volume' in reference to Amazon Web Services? How is it different from other volumes? Is 'boot volume' a standard term used by Amazon?

Is Amazon Elastic Block Storage the one always used as 'boot volume'?

Answer 1

The boot volume is essentially the working storage being used by the instance to utilize operating system code and other files and applications.

Elastic Block Storage (EBS) is a way of providing this boot volume to be used by your instance. Another way is with "instance storage", though that is probably not as popular now.

EBS is nice because it is separate from the processing aspect of your instance, and you can effectively disassociated an EBS volume from your instance and associate a different one, however you like.

EBS isn't always used as the boot volume except for the Micro EC2 instances where it is required. For all other instance sizes IIRC you can choose between EBS or instance storage. EBS is superior in many respects, most of all for the above stated ability to disconnect a volume and have it persist even if you terminate the instance.

Answer 2

In AWS, the boot volume is most often referred to as the "root device". It is analogous to the operating system partition in a standard computer. The term "boot volume" seems to be preferred when talking about importing/exporting VM images in AWS, probably because "root device" is AWS specific, while "boot volume" is more generic. When exporting a VM from AWS, only the boot volume gets exported, not the additional EBS devices.

You can find more information in the AWS EC2 faqs.

Answer 3

Amazon Elastic Block Storage (EBS) is not always used as the 'boot volume'. What Amazon calls the 'local instance store' can be used for boot volume. This disk space is ephemeral (lost when machine shuts down) but most EC2 instances can be launched with an operating system image using this local instance store.