Configuring Mpio - IBM System Storage DS3500 Introduction And Implementation Manual

AIX.fm
q_type
queue_depth
reassign_to
reserve_policy no_reserve
rw_timeout
scsi_id
start_timeout
ww_name

21.2 Configuring MPIO

The following parameters need to be changed when using MPIO with physical devices:
Important: Because this attributes cannot be changed while the device is in active state,
the -perm flag for VIOS and -P for AIX is used so that the change is made in the ODM only.
The changes are applied to the device when the system is rebooted.
Change the fc_err_recov attribute to fast_fail and dyntrk attribute to yes on all the Fibre
Channel adapters. It is possible to use the lsdev -type adapter command to find the
number of the Fibre Channel adapter. Use the chdev command, as shown in
Example 21-6 and Example 21-7 to change the attributes.
Example 21-6 Changing the attributes on VIOS
$ chdev -dev fscsi0 -attr fc_err_recov=fast_fail dyntrk=yes -perm
fscsi0 changed
$ lsdev -dev fscsi0 -attr
attribute
user_settable
attach
dyntrk
fc_err_recov fast_fail FC Fabric Event Error RECOVERY Policy True
scsi_id
sw_fc_class
Example 21-7 Changing the attributes on AIX
# chdev -l fscsi0 -a fc_err_recov=fast_fail -a dyntrk=yes -P
fscsi0 changed
It is very important to change these two parameters. The reason for this is the following:
– Dyntrk: The default for this setting is "no". When set to "yes" it will enable dynamic
tracking of FC devices, and the FC adapter driver detects when the Fibre Channel
N_Port ID of a device changes. The FC adapter driver then reroutes traffic destined for
that device to the new address while the devices are still online. Events that can cause
an N_Port ID to change include moving a cable between a switch and storage device
from one switch port to another, connecting two separate switches using an
inter-switch link (ISL), and possibly rebooting a switch.
– fc_err_recov: This parameter controllers the fast I/O failure and is useful in situations
where multipathing software is used. Setting the fc_err_recov attribute to fast_fail can
decrease the I/O fail times because of link loss between the storage device and switch.
This technique supports faster failover to alternate paths when FC adapter driver
detects a link event, such as a lost link between a storage device and a switch. The FC
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IBM System Storage DS3500: Introduction and Implementation Guide
simple Queuing TYPE
10 Queue DEPTH
120 REASSIGN time out value
Reserve Policy
30 READ/WRITE time out value
0x680000 SCSI ID
60 START unit time out value
0x20480080e51b0c90 FC World Wide Name
value description
switch How this adapter is CONNECTED
yes Dynamic Tracking of FC Devices
0x660c00 Adapter SCSI ID
3 FC Class for Fabric
Draft Document for Review March 28, 2011 12:24 pm
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