The storage system uses Unified LUN Presentation (ULP), which can expose all LUNs through all host ports on both controllers. The interconnect information is managed in the controller firmware. ULP appears to the host as an active-active storage system where the host can choose any available path to access a LUN regardless of disk group ownership. When ULP is in use, the controllers' operating/redundancy mode is shown as Active-Active ULP. ULP uses the T10 Technical Committee of INCITS Asymmetric Logical Unit Access (ALUA) extensions, in SPC-3, to negotiate paths with aware host systems. Unaware host systems see all paths as being equal.
In a typical round-robin configuration, MPIO will load balance between both ports on the server and across all optimized paths to a Volume, however it will never drive I/O down an un-optimized path whilst even a single optimized path remains active. This preferential behavior is an intentional product of the how the Unified LUN Presentation, or ULP feature, takes advantage of Asymmetrical Logical Unit Access, or ALUA extensions, to support optimal path selection to the controller which has ownership of the Volume, and therefore the underlying Pool and Disk Groups.
ULP can make a volume available via any selected array host port so to improve availability and performance, but it is the ALUA protocol which ensures that I/O need not be brokered by a partner controller which would otherwise increase latency. This happens on a per volume level rather than at the array level, and it is for this reason that the array should be configured in a balanced manner, i,e, that I/O is distributed across two equally or at least similarly provisioned pools, and therefore multiple volumes.
In your case as you have two paths so one will be Optimized path and that will show as Active (I/O) and another path will be Active only.
Hope this helps!
Regards
Subhajit
I am an HPE employee
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