RAID 1 (Disk Mirroring)

RAID 1 uses exactly two physical disks and creates a copy (or mirror) of the primary physical disk on the secondary physical disk, as shown in Figure 1.

Table 1 describes RAID 1 across a number of parameters.

Table 1  RAID 1

Parameter

Rating

Description

Read Performance

RAID 1 can perform two read operations simultaneously. Since data is identical on both physical disks, a read command can be sent to the secondary disk when the primary disk is busy with another read operation.

Write Performance

Write performance is comparatively lower than read performance because data (original and mirror) must be written on two physical disks simultaneously.

Fault Tolerance

RAID 1 virtual disks/arrays can tolerate the failure of one physical disk.

Note: Although RAID 1 can tolerate the failure of only one physical disk, it receives high fault tolerance rating because one physical disk in a RAID 1 virtual disk/array (which always comprises of only two physical disks) is equivalent to 50% of the disks. As such, from a purely statistical viewpoint, RAID 1 can tolerate the failure of up to 50% of the physical disks. No other RAID level offers this percentage level of fault tolerance, which explains the high rating for RAID 1. Use this rating after considering the aforementioned limitations of RAID 1 with regard to your application.

Efficient use of disk capacity

Data on the primary disk is mirrored on the secondary disk. Only 50% of the combined physical disk space is available for use.

Automatic rebuild

Available.

Minimum number of drives

 

RAID 1 uses exactly two physical disks.

Suitable Applications

 

RAID 1 is ideally suited for applications requiring high read performance and fault tolerance.

 

Figure 1 describes RAID 1.

Figure 1  RAID 1: Illustration

 

Figure 2 shows a Flash® demo of RAID 1.

Figure 2  RAID 1: Flash® Demo

Note: To view the Flash® demo for RAID 1, install the latest version of Adobe Flash Player at http://get.adobe.com/flashplayer/