Datasheet

38
 Note: The order of the parameters can be changed, as shown, to
facilitate repeating the command and only having to alter the hdisk
number.
 Note: Some of the low end SANs might not handle the larger number of
concurrent commands as well, which can adversely affect performance.
 For redundant VIOS servers, each server needs to be able to access the
same hdisks, so another attribute needs to be set for this:
reserve_policy=no_reserve on each hdisk. Add a space between the
attribute lists on the command.
o lsdev -attr -dev hdisk#, to validate the change.
 Another parameter that can improve performance is the number of I/O commands to
send to the Fibre Channel adapter. The recommended value is 1024. Be sure to change
the value for all ports of all of the FC adapters:
o lsdev -attr -dev fcs#, where # is the FC adapter number you want to display.
o chdev -attr num_cmd_elems=1024 –perm –dev fcs#
o lsdev -attr -dev fcs#, where # is the FC adapter number you want to display to
validate the change.
 To improve reliability, enable dynamic tracking and fast fail over for the LUNs virtualized
to IBM i. Fast_fail should be done only when multiple paths to the disks exist. Do so for
all ports of the all of the adapters:
o lsdev -attr -dev fscsi#, where # is the FC adapter number you want to display.
o chdev -attr dyntrk=yes fc_err_recov=fast_fail –perm –dev fscsi#
o lsdev -attr -dev fscsi#, where # is the FC adapter number you want to validate.
Using the –perm option in these commands means that the value will be updated only in the
VIOS device configuration database (ODM). To make the change effective, reboot VIOS when
there is downtime available for all client partitions.
These settings are applied to each of the fscsiX devices being used. To show the current fscsiX
devices, run the following command:
 lspath
Set the fast fail and dynamic tracking attributes on these devices, run the following command:
 chdev–attr fc_err_recov=fast_fail,dyntrk=yes –perm –dev fscsiX
Next, restart VIOS. The chdev command must be repeated for each fscsiX device but only one
restart is required after all fscsiX attributes have been set.
NOTE: fast_fail is designed for a multipath configuration to not retry failed paths for long periods
of time. In a single path configuration, do not set fast_fail since it will not tolerate temporary
failures on the single path.
To verify the settings have been changed successfully, run the following command:
 lsdev –dev fscsiX –attr fc_err_recov
 lsdev –dev fscsiX –attr dyntrk
 Or just lsdev –dev fscsiX –attr and review the list of attributes shown.
Importantly, the SCSI reserve policy for each LUN (or hdisk) on both VIOS LPARs must be set to
no_reserve to allow disk sharing. Some storage subsystems such as XIV default to no_reserve
and do not require a change, while others such as DS4000 and DS5000 default to single_path.
NOTE: The change must be made prior to mapping the LUNs to IBM i and it does not require a
restart of VIOS.
To show the current reserve policy settings, run the following command:
 lsdev –dev hdiskX –attr reserve_policy
To set the no_reserve attribute if necessary:
 chdev –dev hdiskX –attr reserve_policy=no_reserve
This is done for every hdiskX