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CalDigit T3: 3-HDD RAID-5 (Striping with Parity)
A RAID-5 uses one drive of N for parity information. It can be thought of as a RAID-0 stripe with one parity drive (“striping with parity”), for fault tolerance. Should one drive fail, the RAID degrades to a RAID-0 stripe.
The best speed that can be expected of an N-drive RAID-5 is the speed of an (N-1) RAID-0 stripe, because the parity drive must also be written to. However, even hardware RAID-5 might struggle with that goal; there is some overhead.
Tested with three fast Toshiba 7200 rpm DT01ACA200 series drives. Single-drive speed of the drives used is ~180MB/sec on the fast portion of the drives (left side of graph).
The SoftRAID 5 driver delivers performance right at the best possible speed of around 360MB/sec — impressive. The falloff over the remaining capacity is an unavoidable function of hard drive speed across the capacity (it would not occur with SSDs).