Veritas InfoScale™ Virtualization Guide - Linux on ESXi

Achieving storage availability using Dynamic Multi-Pathing in the hypervisor

When DMP is installed in the hypervisor, DMP allows you to easily provision new storage to ESXi servers. DMP ensures that all available paths to the storage are used, without any additional server-side configuration. The template-based configuration can ensure that the same settings and tuning is applied to each ESX server in an environment.

The following scenario describes a typical use case for storage availability.

You have a storage array with two array side controllers, and two HBA controllers on the host. In a typical SAN configuration, this configuration results in 4 paths to the back-end storage array, and ensures that the loss of an HBA, SAN switch, or array controller does not result in the loss of access to the storage array.

Without DMP, VMware defaults to use the Fixed I/O policy, which usually uses a single path for I/O regardless of the number of paths to the back-end storage array. To change this default behavior, the VMware administrator must change the Path Selection policy on all LUNs on a given host, which is a time consuming process. This process must be performed any time new storage LUNs are provisioned to the host.

Figure: Example of VMware native multi-pathing

By contrast, DMP determines all the paths that may be used for I/O, and makes use of those paths without administrator intervention. As new storage LUNs are added, the administrator does not need to remember to make any changes to the multi-pathing configuration, because the new LUNs under DMP control automatically inherit the same configuration characteristics as the other LUNs in use from the same storage enclosure. This feature reduces the opportunity for mis-configuration, and helps streamline the storage provisioning process.

Figure: DMP optimized path configuration