RAID can be used for availability and for redundancy, but it can also be used for performance. Texas Memory is...
using multiple flash cards configured in an N + 1, RAID 5 scheme. That way, if one card fails, they continue to have the permanency for the flash, and they are using RAM for performance. It's a new variation of a classic RAID 5 array in which cache was used for performance and the drives were used for the permanency and protection.
With flash, you have protection. However, flash is not known for high performance on writes. In fact, the more you write to flash, the more errors are introduced. The hybrid drives leverage the strengths of each media type and balancing the performance and availability that RAID provides.
Check out the entire RAID FAQ guide.