User`s guide

Chapter 1. Overview of RAID and RAID Array 200 Subsystems

EK–SWRA2–IG. C01 1–5

1.1.2.3 RAID 0 + 1

RAID 0 + 1 is a combination of striping and mirroring data, as shown in

Figure 1–3.

RAID 0 + 1 writes data across the drives in the same striping fashion as RAID 0,

and achieves redundancy by mirroring data similar to RAID 1. In RAID 0 + 1,

unlike RAID 1, the data disks are also the mirror disks. RAID 0 + 1 mirrors data

back onto the data disks rotated by 1 drive. Therefore, you can use an odd

number of drives in a RAID 0 + 1 configuration whereas you need an even

number of drives in a RAID 1 configuration.

You can continue to access data in a RAID 0 + 1 configuration with a single

drive failure. However, you can not recover data in the event of multiple drive

failures.

Figure 1–3 RAID 0 + 1

Data/1

Mirror 3

Data

Mirror 1

Data/3

Mirror

SCSI-2

Disk Array Controller

SCSI

SCSI SCSI

Block 2-3 D2

Block 8-9 D2

Block 0-1 M1

Block 6-7 M1

Block 8-9 M2

Block 4-5 D3

Block 2-3 M2

Block 10-11 D3

Block 0-1 D1

Block 4-5 M3

Block 6-7 D1

Block 10-11 M3

In Figure 1–3 each segment is defined as two blocks of 512 bytes each. Also, D1

refers to data disk 1, and M1 to mirror disk 1.