I want crash persistent storage for my instance

Take a look at this - https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/RootDeviceStorage.html

Any data on the instance store volumes persists as long as the instance is running, but this data is deleted when the instance is terminated (instance store-backed instances do not support the Stop action) or if it fails (such as if an underlying drive has issues).

You should use EBS volumes to persist data - https://aws.amazon.com/ebs/

You can also use EBS snapshots to back up your data to S3 - https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/EBSSnapshots.html

You can use AWS Backup for backing up your EBS volumes - https://aws.amazon.com/getting-started/hands-on/amazon-ebs-backup-and-restore-using-aws-backup/