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RETENTION OF LOGICAL PATHS DURING TRANSIENT FC-PH LINK FAILURES

IP.com Disclosure Number: IPCOM000013031D
Original Publication Date: 2002-Mar-21
Included in the Prior Art Database: 2003-Jun-12
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Abstract

A procedure is described which allows a fibrechannel N_Port to retain FC-SB-2 upper level protocol information relating to logical paths after transient link failures. Transient link failures are relatively short link failures which are due to to transient events such as noise bursts or loose cables.

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RETENTION OF LOGICAL PATHS DURING TRANSIENT FC-PH LINK FAILURES

A procedure is described which allows a fibrechannel N_Port to retain FC-SB-2 upper level protocol information relating to logical paths after transient link failures. Transient link failures are relatively short link failures which are due to to transient events such as noise bursts or loose cables.

Distinguishing transient link failures from non-transient link failures has several advantages. First, it allows FC-SB-2 operations to continue normally after transient link failures, and it allows resources to be released after non-transient link failures. Retaining FC-SB-2 logical paths during transient link failures also prevents these link failures from causing errors at the System Control Program, and thereby causing the possible loss of reserves at the device and loss of access to the device. After a non-transient link failure, there is a high probability that the logical paths to a control unit are no longer usable. In this case, a control unit may immediately release resources associated with FC-SB-2 logical paths.

There are two phases in the procedure: a) transient link failure detection, b) transient link failure recovery.

Transient Link Failure Detection

An FC-PH link failure occurs if FC-PH synchronization is lost for at least 100 ms. This can result from transient conditions such as a loose connection or noise burst. There is no reason to reinitialize SB- 2 logical paths after the FC-PH link has been successfully resynchronized. If loss of synchronization remains for an extended period, however, there is a high probability that a more serious problem exists and that reinitialization of SB-2 logical paths will be required to resolve the problem.

For a local link attached to a control unit, a transient link failure is defined as an FC-PH link failure which lasts less than 1.5 seconds (SB_TOV). After this time, an SB-2 link failure occurs. Logical paths are unconditionally removed by a control unit after an SB-2 link failure.

In configurations involving a switch (fabric), a control unit detects a remote FC-PH link failure as follows: (A remote link failure is one which occurs on a link to a channel which is connected to another F_Port on the fabric.) A remote FC-PH link failure at a channel is detected when the control unit receives either 1) a "registered state change notification" extended link service command from the fabric controller which indicates an event has occurred at the channel, or 2) an N_Port login command from the channel. Either of these events indicates that an FC-PH link failure or other problem may have caused a channel to remove a logical path which existed on the link between the channel and the fabric.

Transient Link Failure Recovery

In order to retain SB-2 logical paths after a transient link failure, the following recovery procedure must be performed within a prespecified time period:

1) The N_Port which detected the failure must verify...