A company implemented Automatic Load Balancing (ALB). When the controller workloads are monitored, it becomes obvious that there is an imbalance and…

NetApp Automatic Load Balancing (ALB) is dependent on the Asymmetric Logical Unit Access (ALUA) protocol. For ALB to function correctly, two key host-side requirements must be met. First, the host's multipathing driver must be ALUA-aware and properly configured to recognize and switch between optimal and non-optimal paths as directed by the ONTAP controller. Second, the initiator group (igroup) on the storage system must be configured with the correct host type (ostype). This setting ensures that ONTAP presents the LUNs with the appropriate ALUA characteristics for the specific host operating system. A failure in either of these components will prevent the host from dynamically balancing the load, resulting in the observed imbalance.

A. The "min-min algorithm" is a generic load-balancing concept and not a specific component or requirement for NetApp's ALUA-based ALB functionality.

B. An "adaptive load balancing agent" is a non-specific term; NetApp ALB relies on standard, supported host multipathing drivers (e.g., MPIO), not a proprietary agent.

1. NetApp ONTAP 9 SAN Administration Guide: In the section "How ALUA works

" it is stated

"ALUA is implemented in ONTAP and in the host multipathing software... The host multipathing software queries the target and uses the path-state information to select the optimal paths for I/O." This directly supports the requirement for a compatible host multipath driver (C).

Source: NetApp ONTAP 9 SAN Administration Guide

Page 35

"How ALUA works."

2. NetApp Technical Report 4080 (TR-4080) - SAN Multipathing Best Practices: This report emphasizes the importance of setting the correct ostype for an initiator group. It states

"The ostype setting controls a number of settings

including ALUA behavior... If the ostype is not set correctly

the host might not be able to see any LUNs or might not be able to use all the available paths." This confirms that an incorrect host type configuration (D) can cause pathing and load balancing to fail.

Source: NetApp TR-4080

Page 10

Section 3.1 "Initiator Group Configuration."

3. NetApp Interoperability Matrix Tool (IMT): The IMT is the official source for verifying supported configurations. It provides detailed information on which host types (operating systems)

HBAs

and multipath drivers are validated to work with ONTAP features like ALUA and ALB. An unsupported host type (D) or multipath driver (C) would be identified using this tool as a potential cause for failure.

Source: NetApp Interoperability Matrix Tool (IMT)

accessible via the NetApp support site. (The tool itself is the reference

as specific configurations are user-selected).