Toshiba Magnia 560S - Manual (Page 29)

RAID Overview
Introduction to RAID
11
SCSI-to-SCSI External
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 RAID
product that has two wide SCSI channels operating at speeds up to 320 MB/s must
squeeze the data into a single wide SCSI (320 MB/s) channel back to the host computer.
In SCSI-to-SCSI RAID products, the hard drive subsystem uses only a single SCSI ID,
which allows you to connect multiple drive subsystems to a single SCSI controller.
RAID Overview
RAID is a collection of specifications that describe 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). RAID Controller
Kit-G supports standard RAID levels 0, 1 and 5, and RAID levels 10 and 50, special
RAID versions supported by RAID Controller Kit-G.
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.
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
•
A combination of any two of the above conditions
Consistency Check
In RAID, check consistency verifies the correctness of redundant data in an array. For
example, in a system with dedicated parity, checking consistency means computing the
parity of the data drives and comparing the results to the contents of the dedicated parity
drive.