This saves you also extra downtime. This is one of the latest entries which is out in early beta. More information as well as drivers are available at Dandelion Digital's Linux DAC960 Page . Another very recent entry and currently in beta release is the Smart-2 driver. A number of operating systems offer software RAID using ordinary disks and controllers.
Cost is low and performance for raw disk IO can be very high.
Real cost, performance and especially reliability of software vs. hardware RAID is a very controversial topic. Reliability on Linux systems have been very good so far. RAID Levels RAID comes in many levels and flavours which I will give a brief overview of this here. RAID 0 is not redundant at all but offers the best throughput of all levels here. Data is striped across a number of drives so read and write operations take place in parallel across all drives.