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MegaRAID Express 500 – Host-Based RAID Solution
RAID products are either:
•
host-based or
•
SCSI-to-SCSI
The MegaRAID Express 500 controller is a host-based RAID solution. MegaRAID
Express 500 is a PCI adapter card that is installed in any available PCI expansion slot in a
host system.
Host-Based
A host-based RAID product puts all of the RAID intelligence on an adapter card that is
installed in a network server. A host-based RAID product provides the best performance.
MegaRAID Express 500 is part of the file server, so it can transmit data directly across
the computer's buses at data transfer speeds up to 132 MB/s.
The available sequential data transfer rate is determined by the following factors:
•
the sustained data transfer rate on the motherboard PCI bus
•
the sustained data transfer rate on the i960RM PCI to PCI bridge
•
the sustained data transfer rate of the SCSI controller
•
the sustained data transfer rate of the SCSI devices
•
the number of SCSI channels
•
the number of SCSI disk drives
Host-based solutions must provide operating system-specific drivers.
SCSI-to-SCSI
A SCSI-to-SCSI 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 160 MB/s must squeeze the data into a
single wide SCSI (160 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.
Chapter 2 Introduction to RAID
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