At Risk for an Oracle Audit? We Can Help

vSphere 6 and Oracle RAC

by | Jul 14, 2017 | Oracle, VMware | 4 comments

Jim Hannan (@jim_m_hannan), Principal Architect

Updated on 7/14/17

This week I decided to go back to update this blog. I wrote the blog last year to showcase the new vSphere 6 features for hot adding disks for RAC. The updated screenshots are from vCenter 6.0 Update 2 with ESXi 6.0 Update 2.

Please note: The steps of hot adding a shared VMDK is supported only through the WebUI.

I was fortunate enough to attend the Oracle Expert DBA Workshop with VMware last week. The presentations were excellent and reconnecting with industry experts was professionally very enjoyable. If you’re interested in learning more about the VMware Experts Database Workshop, read Don Sullivan’s blog about the event.

During the workshop I learned about some welcome enhancements added to vSphere 6 that make setting up an Oracle RAC cluster even easier.

Some of standout features, you can utilize through the Web UI, include:

  • Setting the multi-writer flag for VMDKs
  • Setting the multi-writer VMDKs to Independent Persistent (no snapshots, more on this below)
  • Hot adding disks, which is very complementary to Oracle ASM


The link below is very helpful in regards to setting up the multi-writer flag. It also touches on vSAN with RAC. vSAN is VMware’s technology for virtualizing storage and is a great technology that more customers are starting to utilize.

For clarity, I wanted to show that both virtual machines are up and running. From the screenshot below, you can see that vm1 and vm2 are our RAC nodes.

, vSphere 6 and Oracle RAC

Creating and adding disks to Oracle RAC in vSphere 6

First we add the second SCSI controller. All the shared disks will be on this controller.

Add a second SCSI Controller.


We will be using the multi-writer flag to share the disks (a VMware best practice), so the SCSI Bus Sharing should stay set to “None”. The SCSI Controller should also be set to VMware Paravirtual for best performance.


To add hard disks click on the virtual machine Edit Settings.


Expand the shared disk(s) property box by clicking on the arrow.


Below we are adding the required shared disks (VMDKs) for Oracle RAC. Set all shared disks to “thick provisioned, eagerly zeroed” and set the disks to “Independent – persistent”.

  • Thick provisioned, eagerly zeroed disks are thick provisioned, meaning the space is allocated immediately. Eagerly zeroed writes zeroed across the disks, making them immediately ready to start writes for the operating system. Thick provisioned, eager zeroed is a requirement for setting the multi-writer flag.
  • Independent – persistent configure the disks to not be snapshotted when snapshots or backup operations are performed on the virtual machine, which is a VMware best practice for shared disk. In fact, a snapshot against an Oracle RAC cluster will cause problems, and can cause data loss. House of Brick also recommends this setting because it allows for running VM backups on the OS and software disks that are not shared. For example, this would allow Veeam to backup the virtual machine, excluding the Oracle shared disks.


Please note: If you forget to set the multi-writer flag before exiting the dialog box by selecting OK, the sharing parameter will be grayed out and you will not be able to set the multi-writer flag after it has been created. If you do forget to set the multi-writer flag, you can remove the VMDK and start the VMDK creation process over again.

, vSphere 6 and Oracle RAC

Before vSphere 6.0, we had to use PowerCLI scripts to set the VMDKs with the multi-writer flag. Now we can use the WebUI, a terrific new enhancement by VMware. It makes setting up the multi-writer flag simple and quick. Let’s take a look at how to do this using the steps below.

Again, open the disk properties for each of the shared disks and set them to the multi-writer flag for sharing (see the screenshot below).


Finally, when adding the VMDKs to the other nodes you will select “Existing Hard Disk”.

, vSphere 6 and Oracle RAC

And then select the disk.

, vSphere 6 and Oracle RAC

Next, set the multi-writer flag for the second node, SCSI ID, and independent disk.

, vSphere 6 and Oracle RAC

There are a few limitations with running shared disks and the multi-writer flag. Below is a condensed version of the VMware support table that outlines what is supported with multi-writer and what is not. The full table can be found in the VMware knowledge base article, Using Oracle RAC on vSphere 6.x VSAN Datastore (2121181).

VMware Support Table Multi-writer

In this blog, I reviewed the enhancements added to vSphere 6 that make setting up an Oracle RAC cluster even easier. I also updated the content with screenshots from vCenter 6.0 Update 2 with ESXi 6.0 Update 2.


  1. Hi
    Thanks for the detailed document, I followed the steps you mentioned, But I have an issue, File sync between VM on the shared disk.
    For ex:-If a create a file from VM1 / VM2 on the shared disk, that file is NOT visible from other VMs on the shared disk. Do we need to make any fine tuning to get the sync enabled.

    • Thanks for the question. What version of vSphere are you running? What OS version are you running for the guest OS? There is nothing specific that needs to be set for the file system to sync, Oracle Clusterware will handle the writes. If you are trying to create a shared file system between VMs without Clusterware you could do something like NFS (Linux) or a CIFS (Windows) share directly to the guests.

  2. Hi and thanks for the detailed document.
    We had some failure in the past using LPM (AIX) or Live Migrate (OVM) with RAC. Sometimes there was node eviction, so we try to minimize / avoid moving guest/lpar around.

    Do you think that, with the right setup, vMotion is safe with RAC?

    We don’t have very high workload required RAC, it’s more to have better availability. My feeling about it right now is that for the last 5 years, we had some downtime due to RAC (misconfiguration mostly), but it never solved hardware issues – we just didn’t have any. So using RAC sometimes cause problem, but rarely/never prevent non-existant hardware crashes. Is it worth it?
    The only recent reason to have it is to use CDB/PDB and doing “live” maintenance (one node at a time) (OS or CDB or other).

    Any thoughts appreciated!

    – From the unix guy, not the Oracle guy 🙂

    • Thanks for reading our blog. We installed our first RAC instance on vSphere 3. In that time we have not seen or heard about stability issues with vMotion. Additionally some of our customers have replaced Oracle RAC with single instance because vSphere HA offers the high availability requirement that they need.

      We estimate that it takes about 4 minutes or less for the virtual machine to failover in the event of a HA event. CDB/PDB are nice features, but they come at an additional cost. Typically, customers choose to run one database to one virtual machine, it increases patching but gives them flexibility with outages for patching.


Submit a Comment

Your email address will not be published. Required fields are marked *