Information Technology Reference
In-Depth Information
It should be clear now that the M-Series offers highly configurable systems,
allowing the user to configure domains in many different ways.
Given that many consolidation efforts use virtualization tools to aid in the re-
duction of server sprawl, the uptime of the systems and of the individual guest
environments is critical. Many aspects of the M-Series contribute to domain avail-
ability and uptime. While elements such as processor instruction retry, L1 and
L2 cache dynamic degradation, memory Extended-ECC, and partial ASIC failure
recovery automatically benefit all domains, some features are configurable by the
administrator to improve availability:
Memory Mirroring.
The M-Series implements true memory mirroring,
which means that half of the memory on a system board is visible to the do-
main. This happens because the Memory Access Controller (MAC) will write
and read from two memory locations at the same time. The M4000/M5000
mirrors memory in a different way than on the M8000/M9000. Figure 2.11
shows how memory is mirrored on the M4000/M5000—namely, it is mirrored
between the banks that a single MAC manages. For the M4000 and M5000,
memory can be mirrored regardless of the mode of the system board (Uni-
XSB or Quad-XSB). There is no trade-off between memory availability and
domain granularity.
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Figure 2.11
Memory Mirroring on M4000/M5000
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