Fujitsu SPARC Enterprise M8000 Service Manual page 510

Crossbar Unit (XBU_B)
FIGURE B-9
The XBU has the following characteristics.
Only cold replacement is available for the XBU.
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In the M9000 server (with an expansion cabinet) model, control over the expansion
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cabinet is done by connecting the XBUs of both base cabinet and expansion cabinet with
cables.
The XBU has a normal mode and a degraded mode. In normal mode, all eight sets
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operate; and in degraded mode in which a failure has occurred, the four sets containing
the failed set are disconnected, and operation continues with the remaining four normal
sets. If an XB fails, the system is shut down to disconnect the four sets including the
failed XB, and it is then automatically recovered.
A dedicated LSI chip is used for the crossbar switch (XB).
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For the bus connecting CMU and XBU, a high-speed link is used.
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For the bus connecting the IOU and XBU and the bus connecting XBUs of the base
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cabinet and expansion cabinet, a high-speed link is being used.
The XBU has a label bearing the printed component number and manufacture's serial
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number.
B-16 SPARC Enterprise M8000/M9000 Servers Service Manual • October 2012