For io1 volumes—us-east-1, us-west-2, eu-west-1, and ap-northeast-2. Multi-Attach enabled volumes can’t be attached to R5b instances. Standard file systems, such as XFS and EXT4, are not designed to be accessed simultaneously by multiple servers, such as EC2 instances.
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-volumes-multi.html

