Areca 24/4 Internal/External Port Pcie 3.0 12 Gb/s SAS/SATA Raid Controller 2Gb Cache - Manual (Page 262)

APPENDIX
262
Figure G-1, Dual Pass-Through Disks & Triple Pass-Through Disks
regarded as the hard disk clone function, a host’s data will write
simultaneously into two or three hard disks in the RAID controller.
Triple pass-through means “save three copies of the data such
that you can survive two disks failure and still have everything." If
you combine an SSD and HDDs in a mirrored pass-through hybrid
solution, you can get all the reads from the SSD with SSD speed.