.Datastore clusters and Storage Distributed Resource Scheduler (Storage DRS, SDRS) are new features in VMware vSphere 5.
A datastore cluster is a collection of datastores. The Storage DRS feature provides load balancing for a datastore cluster in terms of storage space and I/O traffic. Storage DRS uses Storage VMotion to distribute the virtual disks among the datastores included in the datastore cluster.
If Storage DRS moves the virtual machine disks during backup, the backup may fail or succeed with warnings. To avoid this, you can set up the SDRS Scheduling option for the datastore cluster so that the automation level changes to Manual for the duration of your backup window. For more information about compatibility with Storage VMotion, see the "Support for VM migration" section.
When setting up a destination for a recovery to a new virtual machineor for a regular conversion to a virtual machine, you can select either a datastore cluster or one of its datastores, depending on whether SDRS is enabled:
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