vSphere 5 Storage DRS

Virtual machine provisioning has always imposed operational challenges. Monitoring datastore capacity and I/O load has proven to be very difficult and as a result is often neglected. During the provisioning process of virtual machines and virtual disks, datastores are often randomly selected, leading to hot spots and over- or underutilized datastores. Storage DRS is a new feature introduced in vSphere 5.0. It provides smart virtual machine placement and load balancing mechanisms based on I/O and space capacity. Storage DRS will help decrease operational effort associated with the provisioning of virtual machines and the monitoring of the storage environment.

Datastore Clusters

With vSphere 5.0, a new VMware vCenter™ object called a datastore cluster is introduced. Datastore clusters form the basis of Storage DRS. A datastore cluster is a collection of datastores aggregated into a single unit of consumption from an administrator’s perspective. When a datastore cluster is created, Storage DRS can manage the storage resources comparably to how Storage DRS manages compute resources in a cluster. As with a cluster of hosts, a datastore cluster is used to aggregate storage resources, enabling smart and rapid placement of new virtual machines and virtual disk drives as well as load balancing of existing workloads.

Placement Recommendations

Storage DRS provides initial placement and ongoing balancing recommendations, helping vSphere administrators make placement decisions based on space and I/O capacity. During the provisioning of a virtual machine, a datastore cluster can be selected as the target destination for this virtual machine or virtual disk, after which a recommendation for initial placement is made based on space and I/O capacity. Initial placement in a manual provisioning process has proven to be very complex in most environments. As a result, crucial provisioning factors such as current space utilization and I/O load are often ignored. Storage DRS ensures that initial placement recommendations are made in accordance with space constraints and with respect to the goals of space and I/O load balancing. These goals aim to minimize the risk of storage I/O bottlenecks and the performance impact on virtual machines. 

Ongoing balancing recommendations are made when one or more datastores in a datastore cluster exceed the user-configurable space utilization or I/O latency thresholds. These thresholds are typically defined during the configuration of the datastore cluster. Storage DRS applies the datastore utilization reporting mechanism of VMware vCenter Server, to make recommendations whenever the configured utilized space threshold is exceeded. I/O load is evaluated by default every 8 hours. When the configured maximum space utilization or the I/O latency threshold (15ms by default) is exceeded, Storage DRS will calculate all possible moves, to balance the load accordingly while considering the cost and the benefit of the migration.