First Virtual Communications 3000 user manual RAID Basics, RAID 1 / 0+1

Introduction

The industry standard SCA2 connector is used to interface between the device and the backplane. SCA features staggered contact pins and insertion guidance. All signals such as SCSI, Ids, Power etc. are carried through the SCA. This lowers cost, enhances reliability and fully conforms to the Ultra SCSI specification.

RAID Basics

RAID stands for Redundant Array of Independent Disks3. Some of the advantages of using a RAID storage subsystem are:

∙Provides disk spanning by weaving all connected drives into one single volume.

∙Increases disk access speed by breaking data into several blocks for reading/writing it to several drives in parallel. With RAID, storage speed increases as more drives are added. Without RAID, the speed slows down as more drives are installed.

∙Provides fault-tolerance by mirroring or parity operation.

RAID 0

Block Striping - Data is broken into logical blocks, the size of a SCSI disk block, and striped across several drives.

Drive 0

A0

B0

C0

D0

Table 1-5 RAID 0 layout
Drive 1	Drive 2
A1	A2
B1	B2
C1	C2
D1	D2

Drive 3

A3

B3

C3

D3

Drive 4

A4

B4

C4

D4

RAID 1 / 0+1

Mirroring and Striping - Copy of the same data is recorded into sets of striping drives. In the event of failure, the duplicate set continues operation. Two drives implies a pure RAID 1 solution without the possibility of striping the mirrored drives. The equivalent capacity will be that of a single drive. Four drives will appear with the layout as shown in Table 1-6 with the equivalent capacity of two drives. Six drives will have the equivalent capacity of three drives and so on. An even number of drives is required for this RAID level.

Table 1-6 RAID 0+1 layout

Set 1
Drive 0	Drive 1
A0	A1
A2	A3
A4	B0
B1	B2

Set 2

Drive 0

A0

A2

A4

B1

Drive 1

A1

A3

B0

B2

3RAID Advisory Board Definition

1-9