IBM DS3500 - Page 675

Chapter 21. AIX 6.1 configuration guide 651
Draft Document for Review March 28, 2011 12:24 pm AIX.fm
adapter driver waits a short period of time, approximately 15 seconds, so that the fabric
can stabilize, this occurs when the default setting of “delayed_fail” is set. At that point, if
the FC adapter driver detects that the device is not on the fabric, it begins failing all I/Os
at the adapter driver. Any new I/O or future retries of the failed I/Os are failed
immediately by the adapter until the adapter driver detects that the device has rejoined
the fabric. In single-path configurations, especially configurations with a single path to
a paging device, the delayed_fail default setting is preferred, one such scenario is AIX
server direct attachment to the DS3500 controller host port.
򐂰 To enable load balancing across multiple Fibre Channel adapters within the Virtual I/O
Servers when using the base AIX MPIO support, set the algorithm to round_robin for each
physical disk as shown in Example 21-8 and Example 21-9.
Example 21-8 Setting the round_robin parameter on VIOS
$ chdev -dev hdisk2 -attr algorithm=round_robin -perm
hdisk2 changed
Example 21-9 Setting the round_robin parameter on AIX
# chdev -l hdisk2 -a algorithm=round_robin -P
hdisk2 changed
򐂰 Enable the health check mode for the disk so that the status of the disks is automatically
updated. Health check mode is disabled by default (hckeck_interval=0). As long as it is
disabled the client partition does not update the path status in case of a failure of the
active path. To activate the health check function, use the chdev command, as shown in
Example 21-10 and Example 21-11. In this example, we use a health check interval of 60
seconds. To check for the attribute setting, use the lsattr command.
Example 21-10 Changing the health interval parameter on VIOS
$ chdev -dev hdisk2 -attr hcheck_interval=60 -perm
hdisk2 changed
Example 21-11 Changing the health interval parameter on AIX
# chdev -l hdisk2 -a hcheck_interval=60 -P
hdisk2 changed
All this parameters can also be changed from Smitty mpio  MPIO Device
Management  Change/Show MPIO Devices Characteristics.
Note: It is necessary to set the reserve_policy to "no_reserve" (as shown in Example 21-4
and Example 21-5) before setting the algorithm to round_robin.
Note: MPIO for virtual SCSI devices currently only support failover mode in AIX.
Note: The path switching also works if the hcheck_interval attribute is disabled, but it is
recommended to have the status updated automatically.