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RAID-1 Mirror in Hardware vs Software
For software mirroring, Apple’s Disk Utility has support built-in.
Hardware RAID-1 mirroring is simple with an external dual-drive enclosure that supports it: set the switch to mirror mode, and it’s ready to go.
Dual-drive hardware RAID-1 is the simplest option because the enclosure itself takes care of the RAID issues, presenting itself to the system as if it were a single drive. Initialize it just as you would any single drive.
Shown below is one dual-drive RAID-1 capable unit, the OWC Mercury Elite Pro Dual (it can also be sued for RAID-0 striping or indepedent drives).
See OWC Dual-drive Enclosures Overview for more ideas of what is available.