Veritas InfoScale™ Virtualization Guide - Linux on ESXi

Achieving simplified management using Dynamic Multi-Pathing in the hypervisor and guest

It is very common in VMware environments to have clusters of VMware systems that share common storage and configurations. It is not always easy to keep those configuration in sync across a number of servers, and this can place a burden on the administrators to ensure that the same settings are in place on all systems in the same cluster. DMP for VMware provides a mechanism to create and apply a template across systems to ensure that the same settings are in place. After an administrator configures a single host, the DataCenter View provides the ability to save those settings as a template, and then apply the common template to other hosts in the VMware DataCenter. This mechanism provides an easy and simplified process to make sure that all hosts are identically configured, with minimal administrator intervention.

Figure: DMP tuning template options

With native multi-pathing, administrators must often manually configure each storage LUN to select a multi-pathing policy. Even then, the best policy available is round robin, which does little to work around I/O congestion during unusual SAN workload or contention for a shared storage path.

With DMP, as storage is discovered, it is automatically claimed by the appropriate DMP Array Support Library (ASL). The ASL is optimized to understand the storage characteristics and provide seamless visibility to storage attributes. You do not need to perform any additional management tasks to ensure that all paths to a storage device are used to their optimum level. By default, DMP uses the Minimum Queue algorithm, which ensures that I/Os are optimally routed to a LUN path that has available capacity. Unlike round robin policy, the minimum queue algorithm does not force I/O onto overloaded paths (which round robin would do, as it has no visibility to contention

As you configure or add additional storage, no additional administration is required beyond configuring the storage into a VMware datastore. If you made any optimizations on the storage enclosure, a new LUN automatically inherits the optimizations for that enclosure. You do not need to configure new storage LUNs to use any specific multi-pathing policy. DMP automatically leverages all paths available, with no need for administrator intervention.