2.3.14 Disk Array Types

Table 2.4 describes the RAID disk array types.

Table 2.4

Disk Array Types

 

 

 

Type

 

Description

 

 

 

Software-

 

The array is managed by software running in a host computer

Based

 

using the host CPU bandwidth. The disadvantages associated

 

 

with this method are the load on the host CPU and the need

 

 

for different software for each operating system.

 

 

SCSI to SCSI

The array controller resides outside of the host computer and

 

 

communicates with the host through a SCSI adapter in the

 

 

host. The array management software runs in the controller. It

 

 

is transparent to the host and independent of the host

 

 

operating system. The disadvantage is the limited data transfer

 

 

rate of the SCSI channel between the SCSI adapter and the

 

 

array controller.

 

 

 

Bus-Based

 

The array controller resides on the bus (for example, a PCI or

 

 

EISA bus) in the host computer and has its own CPU to

 

 

generate the parity and handle other RAID functions. A bus-

 

 

based controller can transfer data at the speed of the host bus

 

 

(PCI, ISA, EISA, VL-Bus) but is limited to the bus it is designed

 

 

for. MegaRAID SCSI 320-0 resides on a PCI bus, which can

 

 

handle data transfer at up to 132 Mbytes/s. With MegaRAID

 

 

SCSI 320-0, the channel can handle data transfer rates up to

 

 

320 Mbytes/s per SCSI channel.

 

 

 

2.3.15 Enclosure Management

Enclosure management is the intelligent monitoring of the disk subsystem by software and/or hardware.

The disk subsystem can be part of the host computer or can be separate from it. Enclosure management helps you stay informed of events in the disk subsystem, such as a drive or power supply failure. Enclosure management increases the fault tolerance of the disk subsystem.

RAID Overview

2-11

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