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Disk Array Types
The RAID disk array types are listed in the following table:
Type
Software-
Based
SCSI to SCSI
Bus-Based
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.
16
MegaRAID Express 500 Hardware Guide
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. MegaRAID
Express 500 resides on a PCI bus, which can handle data transfer
at up to 132 MB/s. With MegaRAID Express 500, the channel can
handle data transfer rates up to 160 MB/s per SCSI channel.
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