Areca 24/4 Internal/External Port Pcie 3.0 12 Gb/s SAS/SATA Raid Controller 2Gb Cache - Manual (Page 257)

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APPENDIX
RAID 1 - Multi Mirroring
RAID 1-Multi Mirroring is also known as “triple disk mirror”; data
written on one disk drive is simultaneously written to another
two disk drives. Read performance will be enhanced if the array
controller can, in parallel, access all members of multi mirrored
drives. During writes, there will be a minor performance penalty
when compared to writing to a single disk. If one or two drive
fails, all data (and software applications) are preserved on the
healthy drive. RAID 1-Multi Mirroring writes three copies of ev-
erything, but its data storage capacity effective is 33.3%. HDDs
and SSDs have different characteristics. If you combine an SSD
and a HDD in a RAID1-Multi Mirroring hybrid solution, you can
get all the reads from the SSD with SSD speed and at the same
time have the redundancy of RAID1 without the need to buy a
second, expensive SSD.