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VMFS formats ScaleIO volumes as VMFS volumes.
A VMFS volume consists of the ScaleIO volume number and the disk serial number as seen by the ESX host, which are written back to the new VMFS volume as a header signature.
A VMFS volume does not necessarily have to consume the entire ScaleIO volume, but sharing a ScaleIO volume between multiple VMFS volumes or even another file system through partitioning is poor design and will likely lead to highly unpredictable performance, especially if that VMFS volume is used to support a datastore that houses virtual ASM disks.
VMFS volumes should be created in vSphere to ensure that the start sectors on are properly aligned.