Use Disk Utility To Create A Raid 1 Mirror Array
How Your Mac Works With a RAID 1 Array When your Mac writes data to the mirrored set, it duplicates the data across all members of the set to ensure that the data is protected against loss if any hard drive in the RAID 1 set fails. As long as a single member of the set remains functional, your Mac continues to operate normally, giving you complete access to your data....