HP 316095-B21 - StorageWorks Edge Switch 2/24 Planning Manual page 88

Planning Considerations for Fibre Channel Topologies
Note:
preferred path differs from the current path, if input and output (I/O) is active from the
source port, and if congestion is present on the current path.
Note:
time-out value (R_A_TOV) must be specified for each fabric element.
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Activating a preferred path can result in receipt of out-of-order frames if the
A rerouting delay parameter can be enabled at the Element Manager
application to ensure the director or switch provides correct frame order
delivery. The delay period is equal to the error detect time-out value
(E_D_TOV) specified in the Element Manager application. Class 2 frames
transmitted into the fabric during this delay period are rejected; Class 3
frames are discarded without notification. By default, the rerouting delay
parameter is enabled.
To prevent E_Port segmentation, the same E_D_TOV and resource allocation
E_Port segmentation — When an ISL activates, the two fabric elements
exchange operating parameters to determine if they are compatible and can
join to form a single fabric. If the elements are incompatible, the connecting
E_Port at each director or switch segments to prevent the creation of a single
fabric. A segmented link transmits only Class F traffic; the link does not
transmit Class 2 or Class 3 traffic.
The following conditions cause E_Ports to segment:
— Incompatible operating parameters — Either the R_A_TOV or
E_D_TOV is inconsistent between the two fabric elements.
— Duplicate domain IDs — One or more domain ID conflicts are detected.
— Incompatible zoning configurations — Zoning configurations for the
two fabric elements are not compatible. For an explanation, refer to
"Configuring Zones" on page 156.
— Build fabric protocol error — A protocol error is detected during the
process of forming the fabric.
— No principal switch — No director or switch in the fabric is capable of
becoming the principal switch.
SAN High Availability Planning Guide