Dell POWEREDGE M1000E - Manual (Page 68)

48 Access Gateway Administrator’s Guide
53-1002743-01
Persistent ALPA policy
3
Device Load Balancing policy considerations
• The Device Load Balancing policy should be enabled on the edge AG of a cascaded AG
configuration.
• The Device Load Balancing policy is not applicable on a port group when the APC policy or
Automatic Login Balancing are enabled.
• If a device is mapped to a port that is currently part of a trunk, then the device will use that
trunk. When trunking is used with the Device Load Balancing policy, then the load on each
trunk will be proportional to the number of ports in that trunk. Use the ag -show command to
determine the devices using a particular trunk.
• When using the Device Load Balancing policy, make sure that all ports in the port group have
the same NPIV login limit. If some ports have a lower login limit than the other ports, and there
are many logins to the group, some devices will repeatedly attempt to connect to the device
with the lower limit (because it has the fewest logins) and fail to connect.
Persistent ALPA policy
The Persistent ALPA policy is meant for host systems with operating systems that cannot handle
different PID addresses across login sessions when booting over a SAN. The Persistent ALPA policy
for switches in Access Gateway mode allows you to configure the AG module so that the host is
more likely to get the same PID when it logs out of and into the same F_Port. Because the
Arbitrated Port Loop Address (ALPA) field makes up a portion of the PID, the PID may change across
switch or server power cycles. This policy, if enabled, helps reduce the chances of a different PID
being issued for the same host.
The benefit of this policy is that it ensures that a host has the same ALPA on the F_Ports through
the host power cycle. You can also achieve the same behavior and benefit by setting the same
policy in the main (core) fabric. When this policy is enabled, AG will request the same ALPA from the
core fabric. However, depending on the fabric, this request may be denied. When this occurs, the
host is assigned a different ALPA. The following modes deal with this situation:
• In “Flexible” mode, the AG logs an event that it did not receive the same (requested) ALPA from
the core fabric and brings up the device with the ALPA assigned by the fabric.
• In the “Stringent” mode, if the requested ALPA is not available, the server login will be rejected
and the server port cannot log in to the fabric.
Enabling the Persistent ALPA policy
By default, Persistent ALPA is disabled. You can enable Persistent ALPA using the
ag
--
persistentalpaenable command with the following syntax and with one of the following value
types:
ag -persistentalpaenable 1/0[On/Off] -s/-f[Stringent/Flexible]
• Flexible ALPA assigns an unassigned ALPA value when the ALPA assigned to the device is taken
by another host.
• Stringent ALPA causes the host login request to be rejected by AG if assignment of the same
ALPA is not possible.
To enable Persistent ALPA, use the following steps.