25.22. Configuring Maximum Time for Error Recovery with eh_deadline
In most scenarios, you do not need to enable the
eh_deadlineparameter. Using the
eh_deadlineparameter can be useful in certain specific scenarios, for example if a link loss occurs between a Fibre Channel switch and a target port, and the Host Bus Adapter (HBA) does not receive Registered State Change Notifications (RSCNs). In such a case, I/O requests and error recovery commands all time out rather than encounter an error. Setting
eh_deadlinein this environment puts an upper limit on the recovery time, which enables the failed I/O to be retried on another available path by multipath.
However, if RSCNs are enabled, the HBA does not register the link becoming unavailable, or both, the
eh_deadlinefunctionality provides no additional benefit, as the I/O and error recovery commands fail immediately, which allows multipath to retry.
The SCSI host object
eh_deadlineparameter enables you to configure the maximum amount of time that the SCSI error handling mechanism attempts to perform error recovery before stopping and resetting the entire HBA.
The value of the
eh_deadlineis specified in seconds. The default setting is
off, which disables the time limit and allows all of the error recovery to take place. In addition to using
sysfs, a default value can be set for all SCSI HBAs by using the
Note that when
eh_deadlineexpires, the HBA is reset, which affects all target paths on that HBA, not only the failing one. As a consequence, I/O errors can occur if some of the redundant paths are not available for other reasons. Enable
eh_deadlineonly if you have a fully redundant multipath configuration on all targets.