Information
Apple introduced CoreStorage with 10.7. It is used as the default for formatting on macOS volumes prior to 10.13.
All HFS and CoreStorage Volumes should be encrypted
Rationale:
In order to protect user data from loss or tampering, volumes carrying data should be encrypted
Impact:
While FileVault protects the boot volume data may be copied to other attached storage and reduce the protection afforded by FileVault. Ensure all user volumes are encrypted to protect data.
Solution
Use Disk Utility to erase a disk and format as macOS Extended (Journaled, Encrypted)