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RAID Overview 2-3
Copyright © 2002 by LSI Logic Corporation. All rights reserved.
2.2.2 SCSI-to-SCSI External RAID
A SCSI-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.
2.3 RAID 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.
2.3.1 Physical 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.
2.3.2 Logical 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