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What is RAID in DBMS?

RAID represents Redundant Array of Independent Disks, which is a technology to connect or join multiple secondary storage devices and use them as a single storage media.
RAID comprises of an array of disks in which multiple disks are linked together to achieve different objectives. 

RAID stages that define the use of disk arrays:

RAID 0, RAID 1, RAID 2, RAID 3, RAID 4, RAID 5, RAID 6

1. RAID 0: In RAID 0 stage, a striped array of disks is applied. Each disk receives a block of data to write/read in corresponding. The data is broken down into blocks and the blocks are circulated among disks. 

2. RAID 1: RAID 1 uses mirroring methods. When data is sent to a RAID controller, it sends a duplicate of data to all the disks in the array. RAID level 1 is also known as mirroring and provides 100% idleness in case of a malfunction.

3. RAID 2: RAID 2 saves Error Correction Code using Hamming distance for its data, striped on different disks. Like stage 0, each data bit in a word is saved on a separate disk and ECC codes of the data words are saved on different set disks. 

4. RAID 3: RAID 3 stripes the data onto multiple disks. The equality bit produced for data word is saved on a different disk. This method makes it possible to overcome single disk malfunctions.

5. RAID 4: A whole block of data is written onto data disks in RAID 4 and then the equality is produced and saved on a different disk. Take note that stage 3 uses byte-level striping, whereas stage 4 uses block-level striping. Both stage 3 and stage 4 need at least three disks to apply RAID.

6. RAID 5: RAID 5 writes entire data blocks onto different disks, but the equality bits produced for data block stripe are circulated among all the data disks rather than saving them on a different dedicated disk.


7. RAID 6: RAID 6 is an extension of 5. In this stage, two independent equalities are produced and saved in distributed fashion among multiple disks. Two parities provide further fault tolerance. This stag needs at least four disk drives to execute RAID.

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