Jim Hannan (@jim_m_hannan), Principal Architect
DBAs often ask me about the different layers involved when presenting storage to Oracle ASM on VMware. In the image below, we have diagrammed all the layers involved in presenting storage to ASM. Starting from the bottom is the storage array layer (in green) presenting on volume to the ESXi hosts. The next layer (in blue) is the vSphere VMFS (Virtual Machine File System). VMFS is a clustered file system, which means the cluster file system can be shared across many ESXi hosts. The other layer for vSphere (also in blue) is the VMDK (Virtual Machine Disk), a container presenting a virtual disk to the virtual machine. In orange is the virtual disk, which presents to the virtual machine OS (Operating System). Keep in mind that the virtual disk has the same properties that any regular disk would have. It should be noted however, that we typically partition the disk before handing it to ASM, which makes it clear when presenting new disks that they are already in use. In red is the ASM disk being presented to ASM.
Hopefully this graphic helps you better understand the different layers involved in presenting storage to ASM on vSphere. Feel free to share any questions or comments below.