User Guide

Table Of Contents

Marvell RAID Utility User Guide

Selecting a RAID Level 4-37

4.2 RAID 1 (Mirroring)

RAID1 is known as mirroring because the data on the logical drive is written to a pair of

physical disks, which ensures that identical data appears on both of the physical disks. See

Figure 4-2 for more detail.

Figure 4-2 RAID 1: Mirroring

RAID 1 can increase Read performance. Data is identical on both of the physical disks, so a

read command can be sent to the disk that is not busy, rather than wait for the primary drive

to finish an in-process read. However, RAID 1 does incur a slight drop in Write performance

because both drives must be written to when sending data to the logical drive.

RAID 1 also incorporates fault-tolerance, which allows access to the data even if one

physical disk fails. In addition, if you replace the failed disk with a new physical disk, the

rebuild begins recreating the mirror set of drives, which can be accomplished while the

system continues to function normally.

Note: Mirroring is a technique used for redundancy, so it is important to remember that, for example,

two 80 Gb physical disks (a total of 160 Gb) would only store 80 Gb of original data because the

remaining 80 Gb is required to mirror the original data.

Block 1

Block 2

Block 3

Block 4

Block 5

Block 6

Block 7

Block 8

Block 1

Block 2

Block 3

Block 4

Block 1

Block 2

Block 3

Block 4

Logical Drive

Physical Disk 1 Physical Disk 2

Mirroring