RAID 1.5 From HighPoint: Striping With Parity Data
In theory, the read operation should be almost as quick as they are with a RAID 0. Running in some kind of striping mode, both hard drives are read from simultaneously.
Writing should not give us any improvement, as data still has to be written onto both drives in order to read in a sripe-mode.
In the worst-case scenario, a hard drive gives up the ghost while the system would still run with the second (imaged) drive. The only disadvantage is that all read data has to be taken from only one drive now.
Basically, this method should be as quick at sequentially reading as RAID 0, while writing should be equally fast than with RAID 1.