Storage DRS

Storage DRS builds on the functionality of Storage I/O Control and Storage vMotion, providing the ability to perform automated balancing of storage utilization.  Storage DRS can perform this automated balancing not only on the basis of storage capacity utilization but also on the basis of I/O load balancing.

Like vSphere DRS, Storage DRS is built on some closely related concepts and terms:

• Just as vSphere DRS uses clusters as a collection of hosts on which to act, Storage DRS uses datastore clusters as a collection of datastores on which it acts.
• Just as vSphere DRS can perform both initial placement and manual and ongoing balance, Storage DRS also performs initial placement of VMDKs and ongoing balancing of VMDKs.  The initial placement functionality of Storage DRS is especially appealing because it helps simplify the VM provisioning process for vSphere administrators.
• Just as vSphere DRS offers affinity and anti-affinity rules to influence recommendations, Storage DRS offers VMDK affinity and anti-affinity functionality.

Storage DRS uses the idea of a datastore cluster --- a group of datastores treated as shared storage resources --- in order to operate.  Before you can enable or configure Storage DRS, you must create a datastore cluster.  However you cannot just arbitrarily combine datastores into a datastore cluster; you must follow some guidelines.

VMware provides the following guidelines for datastores that are combined into datastore clusters:

• Datastores of different sizes and performance characteristics can be combined in a datastore cluster.  Although this is possible, it is not recommended unless you have very specific requirements.  Additionally, datastores from different arrays and vendors can be combined into a datastore cluster.  However you cannot combine NFS and VMFS datastores into a datastore cluster.
• You cannot combine replicated and non-replicated datastores into a Storage DRS-enabled datastore cluster.
• All hosts attached to a datastore in a datastore cluster must be running ESXi 5 or later.  Earlier version ESXi and ESX hosts cannot be connected to a datastore that you want to add to a datastore cluster.
• Datastores shared across multiple datacenters are not supported by Storage DRS.