RAID 5
RAID, which stands for Redundant Array of Inexpensive Disks, is about fail-safe high- performance systems for medium and long-term data protection. Conceptually, there are various different storage strategies that have different RAID levels, which are designated with numbers.
RAID level 5, RAID 5, is about" block striping with distributed parity". Unlike RAID 4, in RAID 5 the drives operate independently and the parity blocks are stored distributed across all the disks. In the parity principle, a parity block is obtained from the user data blocks by exclusive-or linking. A RAID-5 controller provides the data blocks with a parity and distributes them to several disks with equal rights. If a user data block is lost, it can be regained by XORing the remaining blocks with the parity block.
For example, if data block "A" is placed on disk HD1 by the RAID 5 controller, data block "B" on HD2, data block "C" on HD3, and data block "D" on HD4, then the parity block P(ABCD) can be placed on disk HD5. For example, the parity block for the following data blocks EFGH can be stored on HD3. The parity blocks are stored on the disk from which no data block has participated in the parity formation. The parity technique provides parity checking with error detection in stored data blocks, but without error correction.
The parity technique speeds up distributed reads because there is no dedicated parity disk. Writing is slower than with a single disk because the write operation always involves a parity update and data must be read before writing.
Usually, RAID 5 uses five disks, one of which is allowed to fail. By distributing the data and parity blocks among the disk drives in the array, much more economical coding of redundant data is possible than with other RAID levels.