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12 Dell PS Series Arrays: Advanced Storage Features in VMware vSphere | TR1066

While Storage DRS is aware of the datastores involved (and also the volumes) it does not identify where

these volumes exist in the PS Series storage system. Prior to initiating a Storage vMotion action on a virtual

machine, Storage DRS consults with the VASA Provider and queries to find out whether the migration of

the virtual machine and its workload would benefit the overall I/O workload distribution of the PS Series

array. If the migration will not result in an improvement in the distribution of the I/O workload (for

example, if the volumes involved reside on the same PS Series group members), the VASA Provider will

inform Storage DRS not to perform the migration. Conversely, if the VASA Provider agrees that the

migration will result in an improvement in the distribution of I/O (for example, if the volumes involved

reside on different PS Series group members), the provider will approve of the migration request. In this

case, Storage DRS leverages Storage vMotion to move the virtual machine and its I/O workload to the

selected datastore.

In another parallel to the classic VMware DRS feature, Storage DRS has the concept of

maintenance mode

When a datastore in a datastore cluster is placed in maintenance mode, the virtual machines and VMDKs

residing on the datastore are moved to other datastores within the datastore cluster through Storage

vMotion. Storage DRS will ensure that the I/O workload and space utilization remains balanced across the

remaining datastores not in maintenance mode.

Storage DRS also has a placement-constraint rule that is enforced during migrations. The default option is

the

intra-VM VMDK affinity rule,

which keeps specific VMDKs of a virtual machine together on the same

datastore. The inverse of that rule, the

VMDK anti-affinity rule

, keeps specific VMDKs on separate

datastores within the datastore cluster. Finally, there is the

VM anti-affinity rule

which prevents certain

virtual machines from sharing the same datastore.