2.2.2SCSI-to-SCSI External RAID

ASCSI-to-SCSI external RAID product puts the RAID intelligence inside the RAID chassis and uses a plain SCSI host adapter installed in the network server. The data transfer rate is limited to the bandwidth of the SCSI channel. A SCSI-to-SCSI external RAID product that has two wide SCSI channels operating at speeds up to 320 Mbytes/s must squeeze the data into a single wide SCSI (320 Mbytes/s) channel back to the host computer.

In SCSI-to-SCSI external RAID products, the disk drive subsystem uses only a single SCSI ID, which allows you to connect multiple drive subsystems to a single SCSI controller.

2.3RAID Overview

RAID is a collection of specifications that describes a system for ensuring the reliability and stability of data stored on large disk subsystems. A RAID system can be implemented in a number of different versions (or RAID levels). MegaRAID SCSI 320-0 supports standard RAID levels 0, 1, and 5, and RAID levels 10 and 50, special RAID versions supported by MegaRAID SCSI 320-0.

2.3.1Physical Array

A RAID array is a collection of physical disk drives governed by the RAID management software. A RAID array appears to the host computer as one or more logical drives.

2.3.2Logical Drive

A logical drive is a partition in a physical array of disks that is made up of contiguous data segments on the physical disks. A logical drive can consist of any of the following:

￿An entire physical array

￿More than one entire physical array

￿A part of an array

￿Parts of more than one array

RAID Overview

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