Explanation
Redundant Arrays of Inexpensive Disks (RAID)
➢ RAID is the use of small-capacity, inexpensive disk drives as an alternative to largecapacity drives common on mainframe computers.
➢ Later RAID has been redefined to refer to independent disks to reflect advances in the storage technology.
RAID Implementation Methods
➢ The two methods of RAID implementation are:
1. Hardware RAID.
2. Software RAID.
Hardware RAID -
➢ In hardware RAID implementations, a specialized hardware controller is implemented either
on the host or on the array.
➢ Controller card RAID is a host-based hardware RAID implementation in which a
specialized RAID controller is installed in the host, and disk drives are connected to it.
➢ Manufacturers also integrate RAID controllers on motherboards.
➢ A host-based RAID controller is not an efficient solution in a data center environment with a
large number of hosts.
➢ The external RAID controller is an array based hardware RAID.
➢ It acts as an interface between host and disks.
➢ It presents storage volumes to the host, and the host manages these volumes as physical
drives.
➢ The key functions of the RAID controllers are as follows:
✓ Management and control of disk aggregations
✓ Translation of I/O requests between logical disks and physical disks
✓ Data regeneration in the event of disk failures
Software RAID -
➢ Software RAID uses host-based software to provide RAID functions.
➢ It is implemented at the operating-system level and does not use a dedicated hardware
controller to manage the RAID array.
➢ Advantages when compared to Hardware RAID:
✓ cost
✓ simplicity benefits
➢ Limitations:
✓ Performance: Software RAID affects overall system performance. This is due to
additional CPU cycles required to perform RAID calculations.
✓ Supported features: Software RAID does not support all RAID levels.
✓ Operating system compatibility: Software RAID is tied to the host operating system;
hence, upgrades to software RAID or to the operating system should be validated for
compatibility. This leads to inflexibility in the data-processing environment.