Administrator Guide

Fabric Watch Administrator’s Guide 63
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Port fencing
7
NOTE
The execution of the portFencing command is subject to Virtual Fabrics (VF) or Admin Domain
restrictions that may be in place. For example, in non-VF chassis environments, the state change
counter of a trunked slave port gets incremented by more than 1 when the master EX_Port changes
its state. Therefore, it is advisable to set the port fencing high threshold for the State Change area
to a value greater than 4 in this environment.
The allowed threshold configuration settings are displayed on a per-class basis. FOP_Port class
thresholds apply to the entire switch. You can set different thresholds for Storage and Host
FOP_Ports if they are on different switches, based on the fabric configuration.
Port fencing configuration
You must configure port thresholds with the portThConfig command before you can enable port
fencing using the portFencing command. Refer to “portThConfig command procedures” on
page 53 for example port configurations, or refer to the Fabric OS Command Reference for
complete inThreshold recommendations for CRC errors and Invalid Words.
You can configure a specified port type or a list of port types to enable port fencing for one or more
areas. Use the all option to indicate all port types or all areas.
Port fencing recommended area settings
Cyclic redundancy check (CRC) errors and invalid transmission words (ITW) can occur on normal
links. They have also been known to occur during certain transitions such as server reboots. When
these errors occur more frequently, they can cause a severe impact. While most systems can
tolerate infrequent CRC errors or invalid words, other environments can be sensitive to even
infrequent instances. The overall quality of the fabric interconnects is also a factor.
NOTE
For Fabric OS versions 7.1.0 and later, the ITW counter includes a physical coding sublayer (PCS)
violation. ITW violations can occur due to an ITW violation, a PCS violation, or both.
When establishing thresholds for CRC errors and Invalid Words, consider the following:
• In general, “cleaner” interconnects can have lower thresholds as they should be less likely to
introduce errors on the links.
FOP_Ports Cyclic Redundancy Checks (CRC)
Invalid Transmission Words (ITW)
Link Reset (LR)
Protocol Error (PE)
State Change (ST)
Class 3 Discard Frames (C3TXO)
E_Ports
EX_Ports
Cyclic Redundancy Checks (CRC)
Invalid Transmission Words (ITW)
Link Reset (LR)
Protocol Error (PE)
State Change (ST)
TABLE 20 Port fencing class and subclass areas (Continued)
Port type Areas supported for port fencing