Hi Mohammed,
My understanding is that SAN full disk encryption allows your data to be encrypted while at rest on disks. The encryption keys are either stored on the subsystem controllers or an external central store. However there might be performance impact with data encrypted continously.
BitLocker is capable of encrypting entire hard drives, including both system and data drives. BitLocker is a volume encryption feature included in Windows Server. It protects at the file volume level so when the database server is online, the volume is unlocked, though not decrypted. If a malicious party would be able to steal your whole drive, they still would not be able to attach and use it.
In short both are different and more info here - selecting-right-encryption-approach
More info over here bitlocker-device-encryption-overview-windows-10
Hope this helps.
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