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AIX, EVA, MPIO and round robin load balancing

Frequent Advisor

AIX, EVA, MPIO and round robin load balancing

I'm reading this in an AIX connectivity guide for EVA systems:
Load Balancing (roundrobin)
Load balanced I/O is now supported. Set the attribute “algorithm” to roundrobin
in addition to setting “reserve_policy” to no_reserve for each hdisk in
order for load balanced I/O to access the array Lun.

algorithm fail_over The load balancing algorithm, “fail_over”, will send all IO
over a single path. All other paths are standby paths. The
load balancing algorithm “round_robin” will send I/O over
all available paths. The attribute, reserve_policy, will need to
be set to “no_reserve” for round_robin to work.

However, in the SAN Reference Guide, September edition:
Sidan 183 i SAN Reference guide, September 17 edition
Table 88 IBM AIX SAN configuration rules:
• When using active/active or active/passive for EVA storage systems, zoning is
required to limit each IBM server HBA access to one controller port per controller,
except for Secure Path for IBM AIX. For specific Secure Path zoning requirements,
contact an HP storage representative.

These two rules seem to contradict each other. If I were to use round robin I/O, wouldn't that mean every other I/O would go to the not owning HSV controller? This is possible, but I'd do the I/O across the mirror port.
Bret Graham
Valued Contributor

Re: AIX, EVA, MPIO and round robin load balancing


That information about zoning to one port of each controller was a restriction for Secure Path some time ago. With the last release of Secure Path for AIX (2.0D SP3), you could present all EVA host ports to the AIX server and Secure Path would choose one host port from each controller. But keep in mind that Secure Path for AIX only supported active-passive.

The information you mentioned above seems to be backward. The single EVA port per HBA only applied to Secure Path and it has never applied to MPIO or AntemetA.

As for MPIO's round_robin load balancing, you could combine path priorities with round_robin to bias I/O to specific host ports on the owning controller.

Best regards,