Introduction
1-9
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 Disks
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. 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.
Table 1-5 RAID 0 layout
Drive 0
Drive 1
Drive 2
Drive 3
Drive 4
A0
A1
A2
A3
A4
B0
B1
B2
B3
B4
C0
C1
C2
C3
C4
D0
D1
D2
D3
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
Set 2
Drive 0
Drive 1
Drive 0
Drive 1
A0
A1
A0
A1
A2
A3
A2
A3
A4
B0
A4
B0
B1
B2
B1
B2
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RAID Advisory Board Definition
