Microsoft SQL Server 2016: A Beginner's Guide, Sixth Edition by Dusan Petkovic

Author:Dusan Petkovic [Petkovic, Dusan]
Language: eng
Format: azw3
Publisher: McGraw-Hill Education
Published: 2016-10-13T16:00:00+00:00

RAID 0 specifies disk striping without parity. Using RAID 0, the data is written across several disk drives in order to allow data access more readily, and all read and write operations can be speeded up. For this reason, RAID 0 is the fastest RAID configuration. The disadvantage of disk striping is that it does not offer fault tolerance at all. This means that if one disk fails, all the data on that array become inaccessible.

RAID 1 (Mirroring)

RAID 1 is the special form of disk striping that uses the space on a disk drive to maintain a duplicate copy of all files. Therefore, RAID 1, which specifies disk mirroring, protects data against media failure by maintaining a copy of the database (or a part of it) on another disk. If there is a drive loss with RAID 1 in place, the files for the lost drive can be rebuilt by replacing the failed drive and rebuilding the damaged files. The hardware configurations of RAID 1 are more expensive, but they provide additional speed. (Also, hardware configurations of RAID 1 implement some caching options that provide better throughput.) The advantage of the Windows solution for RAID 1 is that it can be configured to mirror disk partitions, while the hardware solutions are usually implemented on the entire disk.

In contrast to RAID 0, RAID 1 is much slower, but the reliability is higher. Also, RAID 1 costs much more than RAID 0 because each mirrored disk drive must be doubled. It can sustain at least one failed drive and may be able to survive failure of up to half the drives in the set of mirrored disks without forcing the system administrator to shut down the server and recover from file backup. (RAID 1 is the best-performing RAID option when fault tolerance is required.)

RAID 1 also has performance impacts in relation to read and write operations. When RAID 1 is used, write operations decrease performance, because each such operation costs two disk I/O operations, one to the original and one to the mirrored disk drive. On the other hand, RAID 1 increases performance of read operations, because the system will be able to read from either disk drive, depending on which one is least busy at the time.

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