Disk Array Types

Type

Software-

Based

SCSI to SCSI

Bus-Based

The RAID disk array types are:

Description

The array is managed by software running in a host computer 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.

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.

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. ADAC Ultra2 S466 resides on a PCI bus, which can handle data transfer at up to 132 MB/s. With ADAC Ultra2 S466, the channel can handle data transfer rates up to 80 MB/s per SCSI channel.

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 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.

Chapter 2 Introduction to RAID

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