What cipher mode is used for Elasticache encryption at rest?

Question

I am currently working through some due diligence for use of Elasticache for Redis. I need to understand the encryption standard used and cypher mode.

The following AWS whitepaper [references Elasticache uses AES-512 standard for encryption at rest](https://docs.aws.amazon.com/whitepapers/latest/architecting-hipaa-security-and-compliance-on-aws/encryption-at-rest-1.html?msclkid=6b625190b06c11ec92d66b02d286bbe3)

[This page](https://aws.amazon.com/about-aws/whats-new/2017/11/amazon-elasticache-for-redis-is-now-hipaa-eligible-to-help-you-power-secure-healthcare-applications-with-sub-millisecond-latency/?msclkid=8c3c874eb07211ec9e4838a5c10d9cca) highlights it now meets AES256 standards.

I am not a cryptography expert but as I understand it, the biggest block size for AES is 256. 
Ignoring the AES standard. I am more interested in the cypher mode at this stage.

Does anyone know cypher mode is used? is it XTS?

Accepted Answer

See this whitepaper on encryption in AWS: [AWS KMS Cryptographic Details](https://docs.aws.amazon.com/kms/latest/cryptographic-details/kms-crypto-details.pdf)

"Each volume is encrypted using AES-256-XTS. This requires two 256-bit volume keys, which you can think of as one 512-bit volume key. "

What cipher mode is used for Elasticache encryption at rest?

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