Thread: Raid

Redundant Array of Independent (mistakenly called Inexpensive sometimes) Disks is a scheme that allows multiple hard disks to"be used to create a single unit with features better than what would be attained if they were not a unit. A "RAID controller" contains the circuitry to manage the disks as a single unit. There are differ¬ent RAID schemes. The most popular ones are RAID 0, 1,0+1 and 5.



RAID 0 allows Striping. a scheme where alternate blocks of data is written to different disks. This results in a direct doubling of the write I read speeds. The flip side is that if one of the disks fails. the entire data becomes inaccessible.

RAID 1 offers data redundancy by mirroring the data. In this scheme. the same data is written to both disks. While there is no improvement in performance. from the security standpoint. fail¬ure in one disk will not result in downtime. since the same data is mirrored on the other disk(s). Both the above-mentioned schemes require at least two hard disks to function.

RAID 0 + 1 brings together the benefits of both the schemes. and obviously requires a minimum of four hard disks to function. RAID 5 allows striping. but also stores the parity information of every operation. which can be used to recover data in case of fail¬ure. This scheme requires a minimum of three drives.