DATA MIRRORING The RAID (Redundant Array of Independent Disks)

DATA MIRRORING

The RAID (Redundant Array of Independent Disks)

ABSTRACT

There are various techniques that are used for achieving data recovery by the means of data redundancy. The RAID (Redundant Array of Independent Disks) devices use various data mirroring techniques. The chief advantage of mirroring is that it provides not only complete redundancy of data, but also reasonably fast recovery from a disk failure.

In this document we are going cover the basic idea behind the mirroring techniques.

The mirroring is actually creating another copy of data which can be retrieved immediately after the data loss.

The mirroring techniques help to improve the read performance considerably. The techniques like Network data mirroring, Asynchronous data mirroring and also Remote data mirroring are considered for the discussion in following sessions.

INTRODUCTION

The DATA MIRRORING is an act of copying data from one location to a storage device in real time. Because the data is copied in real time, the information stored from the original location is always an exact copy of the data from the production device. Data mirroring is useful in the speedy recovery of critical data after a disaster. Data mirroring can be implemented locally or offsite at a completely different location.

Mirroring is one of the two data redundancy techniques used in RAID (the other being parity). In a RAID system using mirroring, all data in the system is written simultaneously to two hard disks instead of one; thus the "mirror" concept. The principle behind mirroring is that this 100% data redundancy provides full protection against the failure of either of the disks containing the duplicated data. Mirroring setups always require an even number of drives for obvious reasons.

The chief advantage of mirroring is that it provides not only complete redundancy of data, but also reasonably fast recovery from a disk failure. Since all the data is on the second drive, it is ready to use if the first one fails. Mirroring also improves some forms of read performance (though it actually hurts write performance.) The chief disadvantage of RAID 1 is expense: that data duplication means half the space in the RAID is "wasted" so you must buy twice the capacity that you want to end up with in the array. Performance is also not as good as some RAID levels.