RAID Variants

RAID 1

RAID 1, or disk mirroring, is the process of replicating the data to more than one disk. Both the disks are operational at the same time, so the system can read data from both simultaneously. This enhances the speed of read operations. However, the write operations are slower as the system executes each write operation twice, once on each disk.

RAID 5

A minimum of 3 disks are required for a RAID 5 array. RAID 5 can tolerate even total failure of any drive in the array without losing a single byte of stored data. RAID 5 is block-level striping with distributed parity. Striping and data are distributed by independent read and write operations. In a “write” operation, data to be recorded is striped across all array members interspersed with a parity block and distributed so as to place one segment containing the parity checksum on a different drive within each striping cycle. Sometimes defined as rotating parity, this scheme is the reason why it doesn’t matter which drive in the array fails.

RAID 6

RAID-6 can tolerate the concurrent failure of no less than two hard drives while precluding data loss and system downtime. RAID 6 provides a second layer of redundancy by means of two separate, independent parity blocks within each stripe written to the data storage subsystem array, distributed among each of the active members in the array. Thus, another moniker for RAID-6 is “double-parity RAID”.

This implementation requires a minimum of four individual drives to form an array, but will typically have a significantly larger number of members since performance, fault tolerance, and cost efficiency are all improved relatively with a larger population. RAID-6 requires a RAID 6 controller.