Information Technology Reference
In-Depth Information
So, why choose one over the other if both are ultimately providing raw LUN access? Because the
RDM in the Virtual Compatibility mode fi le off ers the advantage of allowing snapshots to be taken.
By using the Virtual Compatibility mode, you will gain the ability to use snapshots on top of the
raw LUN access in addition to any SAN-level snapshot or mirroring software. Or, of course, in
the absence of SAN-level software, the VMware snapshot feature can certainly be a valuable tool. h e
decision to use Physical Compatibility or Virtual Compatibility is predicated solely on the opportu-
nity and/or need to use VMware snapshot technolog y or when using physical-to-v irtual clustering.
Make sure you document things well when you start using RDMs. Any storage that is pre-
sented to ESXi, is not formatted with VMFS, and has not already been allocated as an RDM will
show up as available storage. If all the administrators are not on the same page, it used to be
very easy to take a LUN that was used for an RDM and reprovision that LUN as a VMFS datas-
tore, effectively blowing away the RDM data in the process. RDMs are now hidden by default
when they are allocated, but we have seen this mistake happen i rsthand, and let us tell you, the
process is very quick to erase any data that is there. We have gone so far as to create a separate
column in vCenter Server to list any RDM LUNs that are coni gured to make sure everyone has
a reference point; similarly you might want to use a tag (explained in Chapter 3, “Installing and
Coni guring vCenter Server”).
Let's keep moving and perform the following steps to coni gure Microsoft Cluster Services
on Windows Server 2008 across VMs on separate ESXi hosts.
Creating the First Cluster Node in Windows Server 2008
Perform the following steps to create the i rst cluster node:
1. Using the vSphere Web Client, create a new VM, and install Windows Server 2008 (or
clone an existing VM or template with Windows Server 2008 already installed).
Refer to Chapter 9, “Creating and Managing Virtual Machines,” for more details on cre-
ating VMs; refer to Chapter 10, “Using Templates and vApps,” for more information on
cloning VMs.
2. Coni gure the VM so that it has two NICs, as shown in Figure 7.6—one for the public
(production) network and one for the private (heartbeat) network. Assign IP addresses
within Windows Server 2008 as needed. Shut down the VM after you have completed the
networking coni guration.
3. Right-click the new VM and select Edit Settings.
4. Click the New Device drop-down, select RDM Disk and click Add, as shown in Figure 7.7.
5. Select the appropriate target LUN from the list of available targets, and then click OK.
We'll remind you again: Make sure you have the correct LUN or you could overwrite
important data!
6. Click the arrow next the New Hard Disk item and next to Location choose “Store with the
virtual machine to keep the VMDK proxy i le on the same datastore as the VM.”
7. Select either Physical or Virtual for the RDM compatibility mode.
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