VM Clustering: SCSI Bus Sharing vs VMFS Simultaneous Writes

I recently worked on a project requiring Oracle RAC Clustering on VMware.   I read VMware’s Best Practices Guide as part of my research and wanted to point out at least  one significant difference between VM setups for Oracle RAC and for Microsoft Cluster Services (MSCS)…

When deploying  Oracle RAC on vSphere, DO NOT enable SCSI Bus Sharing; DO disable VMFS Simultaneous Write Protection.

When deploying MSCS on vSphere, DO enable SCSI Bus Sharing; DO NOT disable VMFS Simultaneous Write Protection.

To satisfy my own curiosity, I am researching the reasons behind the differences in the cluster configurations.

Based on what I have read so far, Oracle RAC will maintain its own write-consistency.  So, it needs to have control over the storage access instead of having VMware enforce locks on the shared disks.  I’m guessing that since Oracle RAC is an application-based cluster, instead of an OS-based cluster like MSCS, it does not need to share the SCSI bus between the VMs.

You can find out more info about these cluster configurations from the following links:

Disabling VMFS Simultaneous Write Protection

Oracle RAC on VMware Best Practices

Microsoft Cluster Services on VMware Best Practices (vSphere 4, vSphere 5)

MSCS confusion article on vReference’s blog

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