Hardware RAID
The hardware-based array manages the RAID subsystem independently from the host. It presents a single disk per RAID array to the host.
RAID controller cards handle all the actual drive communications. The user plugs the drives into the RAID controller and then adds them to the RAID controllers configuration, and the operating system won't know the difference.
Some computer motherboards are claimed to have onboard RAID. This is typically NOT REAL HARDWARE RAID. It is "Fake RAID."
FakeRAID, also known as ‘HostRAID’ has many of the faults of both Hardware and Software RAIDs without any real benefit. FakeRAID is a combination of a specialty system driver and a modified drive controller chip. On almost all consumer grade motherboards on-board RAID will be "Fake" raid. It is possible however to get a motherboard with a dedicated hardware 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.
