When all data paths presented to a Windows server are optimal, the server identifies the paths as Active Optimized (AO) and will default to the Round Robin MPIO policy.
Round Robin spreads read and write I/O evenly over all available AO data paths. Path selection with Round Robin does not consider latency or bandwidth. All available AO data paths are considered optimal.
PowerStore leverages asymmetrical logical unit access (ALUA) to inform hosts whether data paths are optimal or nonoptimal. Data paths presented from a PowerStore cluster to a Windows host will consist either of a combination of optimal paths and nonoptimal paths, or of all nonoptimal paths, depending on the host connectivity option selected.
When a Windows server detects optimal and nonoptimal paths to a data volume, the server will default to the Round Robin with Subset MPIO policy. A Windows server identifies the optimal paths as Active Optimized (AO), and the nonoptimal paths as Active Unoptimized (AU).
See the E-Lab Host Connectivity Guide for Microsoft Windows for the recommended MPIO timeout values.
The PowerStore Manager Host Connectivity Option that you chose for a host server determines the type of paths presented to the host.
In PowerStore Manager, choose one of the following options for each host server.
Choose the option in Figure 57 when a host server is mapped to only one PowerStore system that is local to that host. The host will default to Round Robin with Subset and detect AO and AU paths to the PowerStore system. Use this option for hosts that are not uniformly mapped to both PowerStore systems in a Metro Volume configuration.
Choose the option in Figure 58 when a local host is uniformly mapped to two PowerStore systems separated by metro distance. Metro distance injects latency between the current (local) and remote PowerStore system.
Choose the option in Figure 59 when a remote host is uniformly mapped to two PowerStore systems over metro distance. Greater distance injects more round-trip latency between the current and remote PowerStore system.
Choose the option in Figure 60 when a host is uniformly mapped to two co-located PowerStore systems within the same building or data center with equidistant paths. This configuration provides similar latency and bandwidth for all data paths.
When a Windows server detects optimal and nonoptimal paths to a data volume, the server will default to the Round Robin with Subset MPIO policy.
A Windows server will route I/O traffic over all AO paths with Round Robin. AU paths are not used unless all AO paths become unavailable. When no AO paths are available, the server will route I/O traffic over all available AU paths with Round Robin. The server will resume using AO paths once one or more AO paths become available.
Allow Windows hosts to automatically detect the type of PowerStore data paths (and default to Round Robin with Subset) as a best practice.
You can override the default MPIO behavior if your workload or situation requires it. Use the Microsoft mpclaim command line utility to configure a host to use a specific MPIO policy if Round Robin with Subset is not wanted.
Verify the behavior of altered MPIO policies or time-out settings in a test or development environment before doing so in production.
For more information see the Dell PowerStore: Microsoft Hyper-V Best Practices white paper on the Dell PowerStore Info Hub.