Had to replace a failed ssd which was part of a mirrored RAID set in a Late 2012 Mac Mini. It was running MacOS 10.11 El Capitan, so the RAID functionality that used to be part of Disk Utility was not available through the app. Apple’s simple RAID tools are still available in terminal, using the command:

diskutil appleRAID <raidverb>

Options for <raidverb> include list and repairMirror.