Software RAID
Software RAID is a form of RAID (redundant array of independent disks) performed by utility software in the operating system. There is no need for a hardware RAID controller card. Drives are connected directly to the motherboard without a RAID controller.
RAID configurations
- RAID 0 – Block level striping. MD can handle devices of different lengths, the extra space on the larger device is then not striped.
- RAID 1 – Mirror.
- RAID 4 – Like RAID 0, but with an extra device for the parity.
- RAID 5 – Like RAID 4, but with the parity distributed across all devices.
- RAID 6 – Like RAID 5, but with two parity segments per stripe.
- RAID 10 – Take a number of RAID 1 mirrorsets and stripe across them RAID 0 style.
RAID 10 is distinct from RAID 0+1, which consists of a top-level RAID 1 mirror composed of high-performance RAID 0 stripes directly across the physical hard disks. A single-drive failure in a RAID 10 configuration results in one of the lower-level mirrors entering degraded mode, but the top-level stripe performing normally (except for the performance hit). A single-drive failure in a RAID 0+1 configuration results in one of the lower-level stripes completely failing, and the top-level mirror entering degraded mode. Which of the two setups is preferable depends on the details of the application in question, such as whether or not spare disks are available, and how they should be spun up.
