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Enable Fast I/O Failure for FC adapt

AIX 5.2 supports the Fast I/O Failure feature for Fibre Channel devices in case of link events in a switched environment. If the FC adapter driver detects a link event (for example, a lost link between a storage device and a switch), the FC adapter driver waits a short period of time, about 15 seconds, to allow the SAN fabric to stabilize. At this point, if the FC adapter driver detects that the device is not on the SAN fabric, it begins failing all I/O requests at the adapter driver level. Any new I/O request, or future retries of the previously failed I/Os, are failed immediately by the adapter, until the adapter driver detects that the device has rejoined the SAN fabric.


Fast I/O Failure is controlled by a new fscsi device attribute, fc_err_recov. The default setting for this attribute is delayed_fail, which is the I/O failure behavior that has existed in previous versions of AIX. Setting this attribute to fast_fail enables Fast I/O Failure, as shown in Example 3-12.

Example 3-12 FC adapter fast_fail option

{node1:root}/_> chdev -l fscsi0 -a fc_err_recov=fast_fail

The fscsi0 device is used for storage data transfer and is a child device of fcs0 (the FC adapter):

+ fcs0 U0.1-P1-I4/Q1 FC Adapter* fscsi0 U0.1-P1-I4/Q1 FC SCSI I/O Controller Protocol DeviceFast fail logic is invoked when the adapter driver receives an indication from the switch that there has been a link event involving a remote storage device port via a Registered State Change Notification (RSCN) from the switch.

Fast I/O Failure may be desirable in situations where multipath software is being used. Setting fc_err_recov to fast_fail may decrease the I/O fail times due to link loss between the storage device and switch and allow faster failover to alternate paths.

In single-path configurations, especially in configurations with a single path to a paging device, the default delayed_fail setting is recommended.

Fast I/O Failure is only supported in a switched environment. It is not supported in arbitrated loop environments, including public loop.

We configured Fast I/O Failure since we were using the Subsystem Device Driver, two adapters per node and two paths to the storage subsystem.

The requirements for Fast I/O Failure support are the following:

FC 6227 adapter firmware - level 3.22A1 or greater

FC 6228 adapter firmware - level 3.82A1 or greater

FC 6239 adapter firmware - all firmware levels

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