If you currently have a RAID setup with hard disk drives, as a rule of thumb it is best not to add a solid state drive to the array. Doing this will slow down performance. Perhaps think about installing the operating system onto the SSD as the boot drive and use the HDDs for storing your data? When creating a RAID setup all the drives in the array should maintain the same architecture.

The performance of a RAID-0 is governed by the weakest link – that is the drive in the array with the slowest read/write speeds. Therefore by adding a SSD to the array you will not benefit from the increased performance of the SSD. Also if there are any problems and the RAID fails, chances are you may well lose all your data! The total capacity is governed by the drive with the smallest capacity. Hence is you RAID two drives of 120Gb and 240Gb, the RAID’s total capacity will be 120Gb times two.

There are no benefits to adding a SSD to a RAID populated by HDDs. You need to use the same type of drives, with the same architecture collectively and think about redundancy should a drive fail?

Having said all of this, there are hybrid RAID solutions out there that combine HDD and SSD technology. Essentially they perform read operations from the faster SSD and write operations from both the SSD and HDD. Adaptec RAID adapters such as the Series 8 and Series 8Q take care of this automatically. The result is a higher number of read operations each second with no degradation in performance of write I/O operations.