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VMware - Cluster of VM and physical server

The vSphere 6 documentation describes how to "Cluster Physical and Virtual Machines" for say MS SQL cluster:
http://pubs.vmware.com/vsphere-60/index.jsp#com.vmware.vsphere.mscs.doc/GUID-78401893-B900-464B-B451-7BF04304A917.html

In the sub-section 'Add Hard Disks to the Second Node for a Cluster of Physical and Virtual Machines', it states:
"...expand SCSI controller and select the SCSI Bus Sharing drop-down menu. Set SCSI Bus Sharing to Virtual and click OK."
(This 'Virtual' setting allows sharing of virtual disks on the same server while 'Physical' setting would allow sharing of vDisks on different servers as well.)

Selecting "Virtual" or "Physical" Bus Sharing makes little sense to me since we are not creating a cluster of two VMs, so there is no sharing of Virtual disks. I will be using RDMs, which will be shared with a physical server. Am I wrong?

Let me add that using RDM seems better (direct and simple) to me than using iSCSI initiator inside the Windows VM, as RDMs bypass the vSwitch. Thanks.

AK
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Akulsh
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Akulsh
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
In that document, it's referring to Cluster in a Box, e.g. two virtual machines on the same host, and you share a VMDK on the host.

If you want to simply Cluster a Virtual and Physical machine, use the Software iSCSI initiator in the VM, and connect direct to the SAN, and create LUNs for virtual and physical machines.

NO RDMs required,


iSCSI Network Traffic can then pass through your dedicated iSCSI switches, e.g. where the VMkernel Portgroup resides handling your storage network, some of our clients have been doing this since 2004, for Microsoft Failover Clusters.

Most actually believe RDM's are more complicated, and are often only used to support Failover Clustering.
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AkulshAuthor Commented:
So are you agreeing with me that 'SCSI Bus Sharing' need not be changed from default 'none' when there is one VM and one physical server in a cluster?

About RDMs, we have to agree to disagree. Their setup seems so simple and direct to me. Thanks.
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Virtual SCSI Bus sharing is Cluster in a Box, sharing of VMDKs, not suitable for physical and virtual.

You need to use RDMs to cluster a physical and virtual server.

if you are referring to virtual or physical RDMs (not virtual or physical VMs)

see here

Difference between Physical compatibility RDMs and Virtual compatibility RDMs (2009226)

this was written about RDM many years ago...

RDM versus VMDK performance

Conclusion: VMFS and RDM have similar performance. Don’t choose RDM for performance.
Source:http://www.vfrank.org/2011/03/22/performance-rdm-vs-vmfs/
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AkulshAuthor Commented:
What would E-E be for VMware related questions without Andrew?
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Thanks for your kind words.
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AkulshAuthor Commented:
I wanted to clarify that I am advocating use of RDMs only in case of a Microsoft cluster. In all other instances, VMFS are of course the way to go.
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
RDM is the recommended best practice!
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