High Availability; Reliability - IBM 2109 Model M12 User Manual

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Cable Side
Figure 5. 2109 Model M12 (cable side and noncable side)

High availability

If a system is available, it is accessible 7 days a week and 24 hours per day.
Availability is designated in terms of 9s. For example, the architecture of the 2109
Model M12 is designed for availability in excess of 99.999%.
The high availability software architecture of the 2109 Model M12 provides a
common framework for all applications that reside on the system. High availability
allows global and local states to be maintained so that any component failure is
fully manageable.

Reliability

In addition to being available, the system must be reliable. This means that some, if
not all, of its state must be maintained. In a reliable system, you are not aware of
the internal state of a switch, and you experience continued system service with
zero degradation.
The 2109 Model M12 provides the following features to ensure reliability:
v An error detection and correction mechanism to protect all data in the switch
v Power-on self test (POST)
v Error detection and fault isolation, such as cyclic redundancy checking (CRC),
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IBM TotalStorage SAN Switch: 2109 Model M12 User's Guide
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parity checking, checksum, and illegal address checking
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Non-cable Side
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