Data Recovery

RAID provides data protection for your server

English: RAID 5 with these four disks (disk 0, 1, 2, and 3) and each group of blocks (orange, yellow, green, and blue) have a distributed parity block that is distributed across the four disks. (Photo credit: Wikipedia)

RAID, an acronym for redundant array of independent (or inexpensive) disks. It refers to a collection of hard disks that are connected in such a manner that provides redundancy, so if one drive fails, data is not lost. Different types of RAID are classified by numbers. The most commonly implemented RAID classes are 0, 1, 5 and 6.

RAID relies on disk striping, parity and in some cases, mirroring, to provide protection against data loss. Disk striping refers to data being placed across multiple disks in a sequential manner. Parity refers to extra data that is stored to assist with protecting and restoring data. Disk mirroring involves multiple disks that contain exactly the same data. RAID5 and RAID6 both involve disk striping and parity. Neither uses disk mirroring.

What is RAID5?

RAID5 refers to a type of RAID that involves block-level disk striping with distributed parity. In this configuration, every drive except one must be functional for the RAID to be operational. If a second drive fails, data loss is likely to occur. Block-level disk striping refers to blocks of data being stored sequentially across drives. Blocks include multiple bytes of data. Distributed parity refers to parity data spanning across all drives in the array, not just being stored on a separate disk. RAID5 is supported by FreeBSD, Linux, Microsoft Windows server operating systems, NetBSD, OpenBSD, OpenSolaris and Solaris 10.

What is RAID6?

RAID6 refers to a type of RAID that involves block-level striping with distributed parity. However, the major difference between RAID5 AND RAID6 involves the degree of distributed parity. RAID6 has double distributed parity. In this configuration, two drives may fail and the array will still be functional without data loss. This provides extra time compared to RAID5 to replace a disk if one fails. However, an additional disk is required for the array to operate. RAID6 is ideal for systems that cannot afford any amount of downtime. RAID6 is supported by Linux, Microsoft Windows server operating systems, OpenSolaris and Solaris 10. It is not supported by NetBSD, FreeBSD or OpenBSD at this time.

What is RAID5+1?

RAID5+1 is a hybrid RAID configuration based off of RAID5. It is sometimes referred to as RAID53. RAID5+1 has block-level disk striping with distributed parity. However, unlike RAID5, the data is also mirrored. This means that in large arrays, many more disks are needed to store the mirrored data. RAID5+1 implementations are rare.