Sagemaker, EFS and EC2

Studio Classic uses Elastic File System (EFS) for storage, see this documentation - https://docs.aws.amazon.com/sagemaker/latest/dg/notebooks.html. So, each Studio Domain you create automatically creates an EFS volume for storage - this is expected behavior.

The docs you linked, https://docs.aws.amazon.com/sagemaker/latest/dg/domain-custom-efs.html, talks about bringing a custom EFS volume to the new Studio. This could be any EFS volume you have, as long as the prerequisites mentioned in the doc are satisfied.

If you create your own EFS, you can use the documentation above to attach it to the new Studio apps. You simply provide the custom file system configurations for the domain, or users, and SageMaker will attach the file system for you. Studio Classic does not allow users to bring their own EFS volume.

Lastly, if you wanted to mount the Studio created EFS to EC2 instance, that is possible. Make sure the security groups allow traffic, and there are mount targets for the EFS volume in the appropriate subnets. This doc walks through the process in detail - https://docs.aws.amazon.com/efs/latest/ug/wt1-getting-started.html