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EMC Symmetrix DMX-3 Product Guide
Data Integrity, Availability, and Protection
Link control cards The LCC is the heart of the Symmetrix DMX-3 disk Fibre Channel
loop and constantly monitors the loop for Fibre Channel layer 0/1
signal connection and protocol errors. If errors are detected, the
controlling software program is notified and, if necessary, the bypass
circuits may be used to switch out the failing loop segments, thereby
allowing the remaining devices on the loop to operate unaffected.
Each disk enclosure, which contains up to 15 individual disk drives,
contains a pair of LCCs.
Each LCC connects one of the ports of the 15 drives to a disk director.
For each disk connection, a bypass circuit is provided and allows that
disk connection to be shunted. This only occurs when the drive is not
installed, the drive was just powered on, the drive was reset, or the
drive is malfunctioning. In addition to the bypass circuits themselves,
the card contains real-time monitors embedded within the loop that
can determine if bad data is being generated on the loop. These
monitors report status to the loop control software and can be useful
in determining which parts of the loop are being affected by potential
hardware failures. The LCC also has the ability to control power to
the drives, and it maintains basic configuration information so that if
the loop configuration is changed (a new disk assembly is inserted,
for example), it reports this to the control software program so that it
may take the appropriate action. The LCC is located within the disk
enclosures, which allows replacement in the case that the isolation
device itself fails. Each port of a disk is connected to a different LCC
(A or B), so access to the data is maintained even during service
operations. Figure 38 on page 167 is an illustration of the back-end
redundancy of the Symmetrix DMX-3 system.
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