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DuraStor 412R/6320SS/7320SS Installation and User's Guide
Each controller sends heartbeat messages via the SCSI buses to its
partner controller. If a controller does not receive a heartbeat
message within a set time period, it will kill the other controller
assuming that it has malfunctioned. After killing the other
controller, it will take ownership of the arrays and will activate its
passive host port to assume the defunct controller's identity.
Warning: The controllers communicate with each other using
SCSI Initiator IDs 6 and 7 on each of the disk channels. You
should not change these ID settings.
Advantages:
Transparent fail-over and fail-back.
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Single point of failure is the host system. (There are no single
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points of failure when dual host systems are configured with
clustering software.)
Upstream fail-over.
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Disadvantages:
Lower performance than the active-active mode.
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Upstream fail-over requires third-party software.
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Careful administration is necessary because all the arrays are
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reported twice to the host operating system, which must use
third-party file share/file lock software to prevent data
overwrites.
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