By – Mohammed Zaid Qureshi.

“Disk mirroring, also known as RAID 1, is the replication of data to two or more disks.”

Disk Mirroring

As all drives are operational, data is read from them at the same time continuously, that results in reading operations being really quick. The RAID array will work even if one drive is in working condition. Write operations, are slow as all write operations are done two times.

If a drive malfunctions, the data is safe on the second disk and the continues to service the host’s data requests from the remaining disk of a pair. When the malfunctioned disk is replaced with a new one, the data copied by the controller from the remaining disk of the mirrored couple.

Mirroring allows quick recovery if a disk malfunctions. But, disk mirroring gives only data protection and it is not a replacement for data backup. Mirroring continuously fetches alterations in the data, on the other hand, a backup captures point-in-time images of the data.

Mirroring includes copying of data — the proportion of storage capacity required is double the amount of data being stored. Hence, mirroring is considered costly and is recommended for important softwares that cannot afford the risk of any data loss. Mirroring increases read performance as read requests can be processed by both the disks. But, write performance is a bit lower than that in a single disk because each write request is processed twice as two writes on the disks.

Mirroring is either software or hardware based. Hardware-based mirroring is applied by using RAID controllers in the system to which different hard disks are connected. At the cost of little system performance deterioration, fault tolerance is introduced to the system.

Conclusion:

Disk Mirroring can provide data protection but at the cost of write performance, but it can increase the read performance significantly. It is costly and is only used for very important files. Hence it should be used wisely.

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