How can an EBS volume that is currently attached to an EC2 instance be migrated from one Availability Zone
Simply create a new volume in the other AZ and specify the original volume as the source.
Detach the volume, then use the ec2-migrate-volume command to move it to another AZ.
Create a snapshot of the volume, and create a new volume from the snapshot in the other AZ.
Detach the volume and attach it to another EC2 instance in the other AZ.