1st is the placement for the 2 node cluster virtual machine, which you should consider split the 2 virtual machine in different host and disable the DRS or vMotion for the cluster node. Now is about the quorum disk and data disk you would like to put in the cluster. You may consider using RDM for either physical or virtual mode, and provide separate SCSI controller for the share disk. You will further require configure the SCSI controller as physical mode allow the RDM to be access by the 2nd node later.

You may not able to add the RDM to the 2nd node as you usually did in this case. You will need to browse through the existing virtual disk, to point it to the vmdk configuration files which own the RDM path from the virtual machine folders.  Once you have done this, you can configure your Microsoft cluster as usual. Not complicated, it just few important steps you need to take note here.

In a test yesterday, we found that a offline VM migration will auto convert the RDM which attach to the virtual machine to the VMDK format when I selected the data store to be moved in offline mode. This was really surprise myself and simplify my work actually, as I do not require some manual file transfer from the RDM to the new virtual disk.

To enable this on ESX host, you need to browse to the configuration tab of the ESX host, and right click the data store and select properties, and click on manage paths option in the GUI wizard. Click on Change button after that, and choose the Round Robin (Experimental) option and click OK. You will need to go through this process 1 by 1 to ensure you had round robin from each ESX host to each of the VMFS Data store.

For VM Guests, Just right click the VM and choose edit setting, and select to the hard disk which has shown as Mapped Raw LUN on the summary tab. Click on the Manage Paths and follow by the change button, and same you can easily configure to have the Round Robin enable.

ESX Host Configuuration

Wizard View for each Data Store connection from ESX

Policy Option which allow to change for Round Robin

Select the option of Round Robin

VM Guests Configuration

Click on Manage Paths to continue with the Round Robin Option in the next screen

You will actually see the same display and option at the last 2 steps compare the VM guests and ESX Host

As for the today, more users are actually deployed the mission critical and high I/O servers on the virtualization environment, but we do see some I/O bottle neck which cause by the storage performance always. VMDK do provide flexibility from management perspective, but it does sacrifice the performance you may require for your databases, files transfers and disk performance. I had run a couple of test with real case scenerio instead of I/O meter that been always use widely, and here is the summarize result I would like to share.

In disk perfomance, we always split it to 2 categories as sequential and random I/O. in sequential mode, you will see the huge different while you try to perform the file transfer locally or through network. My test environment is running with SAN storage from fiber channel with same LUN size and raid group which are created from the Storage Level. The only differences is VMFS Vs Raw.

Raid Group design 7+1 raid 5 configuration and run on MetaLun configuration

Each LUN size is 300GB

Performance monitoring tools = Virtual Center Performance Chart

VM Test Machine = 4 Vcpu, 8GB Memory

Operating System = SLES 10 x32, x64 ; Windows Server 2003 x32, x64

Sequential : RDM is out perform VS VMFS as it able to achieve > 2 times higher through put during the file transfer locally on the VM

Random I/O : The Raw Device Mapping is still out perform the VMFS and getting the similar through put with sequential file transfer. Multi session with random database query is been executed in the test

for NFS file transfer from VMFS to VMFS, I do see the bottle neck happen much more earlier than RDM.

Highest I/O rate for RDM = 180MB/s as during sequential files copy and DB query

Highest I/O rate for VMDK = 100MB/s during sequential files copy and DB query