From GCP docs:
Cloud Storage manages server-side encryption keys on your behalf using the same hardened key management systems that we use for our own encrypted data, including strict key access controls and auditing. Cloud Storage encrypts user data at rest using AES-256, in most cases using Galois/Counter Mode (GCM). There is no setup or configuration required, no need to modify the way you access the service, and no visible performance impact. Data is automatically decrypted when read by an authorized user.
Problem text in bold above (in most cases). From other docs, it appears some legacy HHDs use AES-CBC and AED-CTR (128 and 256 bits). How do we determine/confirm storage encryption is AES and that CBC is not used in a particular data center?