Home > Blogs > Virtualize Business Critical Applications

Setting Multi Writer Flag for Oracle RAC on vSphere without any downtime

Oracle RAC Cluster using ASM for storage would require the shared disks to be accessed by all nodes of the RAC cluster.

The multi-writer option in vSphere allows the VMFS-backed disks to be shared by multiple VM’s simultaneously. By default, the simultaneous multi-writer “protection” is enabled for all .vmdk files ie all VM’s have exclusive access to their .vmdk files. So in order for all of the Oracle RAC VM’s to access the shared vmdk’s , the multi-writer protection needs to be disabled.

KB Article 1034165 provides more details on how to set the multi-writer option manually to allow VM’s to share vmdk’s (link below).

The above method would require the VM’s to be powered off before the multi-writer option can be set in the .vmx configuration file. This means that the Oracle RAC instance would have to be shutdown and the VM completely powered off before the option can be set leading to an Instance outage.

Oracle DBA’s would rather a method where they could add shared disks on the fly to a running Oracle RAC cluster without any downtime.

A colleague and I working for VMware PSO some time back (now I have moved under the Global Center Of Excellence group ) wrote a POWERCli script called the “addSharedDisk” which adds a new shared disk to the existing Oracle RAC nodes along with setting the multi-writer flag setting , setting the disks as independent-persistent and eager-zero thick formatting.

This script can be used to add shared disk on the fly while the Oracle RAC Clusters is up and running thus avoiding any outage.

– This is an generic script provided and can be customized as per your requirement
– This script is provided for educational purposes only , please use at your own risk
– No Support will be provided for this script
– All values provided in this script is for example only, you would need to provide real values

This script accepts at the command prompt
– The number of shared disks to be created( maximum 55)
– The number of nodes that you need this shared disk be added to

-the script places all shared VMDK files in the same datastore as the boot disk VMDK files. This can be customized to place shared vmdk’s on different datastores for IO load balancing
-the script can be further customized to place vmdk’s on different SCSI controllers.
-the script has the logic to check the network requirements of the Oracle RAC interconnect adapters(assumption of the script is 2 Private Adapters are deployed per VM) . (can be removed or commented out if not required)

The script can be found in the link below [https://communities.vmware.com/docs/DOC-24873]


This entry was posted in Uncategorized on by .
Sudhir Balasubramanian

About Sudhir Balasubramanian

Sudhir Balasubramanian is a Staff Solution Architect specializing in all Oracle Technologies on VMware SDDC stack.

Prior to joining VMware in 2012 , Sudhir has worked for close to 20 years as a Principal Oracle Database Administrator (DBA) / Architect in Oracle Technologies for fortune 100 companies including Tata Consultancy Services (TCS) , Sony Electronics, Epsilon Marketing (Aspen/Newgen), Teletech Corp, SAIC, Active Network and Sempra Energy Holdings before joining VMware PSO before moving into the Global Field and Partner Readiness (GFPR) and now in CPBU TMM.

Sudhir is also experienced in EMC SAN Technologies & Unix/Linux Operating Systems along with being a VMware vBCA Specialist , VMware vExpert and VMware VCA – Cloud certified.

Sudhir is also an Oracle ACE.

Sudhir is a recognized Speaker having presented at Oracle Open World, IOUG, VMworld, VMware Partner Exchange, EMC World, EMC Oracle Summit and various Webinars and is an Industry recognized expert in Oracle Virtualization technologies.

Sudhir has also co-authored a book “Virtualizing Oracle Business Critical Databases on VMware SDDC” which is a comprehensive authority for Oracle DBA ’s on the subject of Oracle & Linux on vSphere.

Sudhir regularly blogs at the official VMware Application blog site

Sudhir also blogs on his personal website

Sudhir holds a degree in Master of Computer Science from San Diego State University (SDSU) graduating in 2011.

Twitter @vracdba

12 thoughts on “Setting Multi Writer Flag for Oracle RAC on vSphere without any downtime

  1. Iwan 'e1' Rahabok

    Awesome. Could you explain why/how a PowerCLI script can do away with the downtime? I think the magic is not in the script, but in the method. So would be grateful if you explain the actual method/technique used.
    Thanks from Singapore.

    1. sudhir

      Could you explain why/how a PowerCLI script can do away with the downtime : In order to set the multi-writer flag as explained above in any RAC VM , you would have to use the GUI via configuration options and set the flag in the key-value table which makes the changes in the .vmx file. if the VM is powered on, the config button is greyed out ie you are not allowed to make changes via the GUI. so you would have to shut down VM which means shut down the apps running in those VM’s

      The magic is in the method which is deployed in the scripts. Did you get a chance to read thru the script I posted ?


  2. Bryan Wood

    The C# client enforces a restriction that you cannot make the needed edit while the VM is online. But through the SDK API, that restriction is not enforced. By building up a customization spec structure, we can set the additional parameter for N number of disks without downtime.

    Bryan Wood

    1. Sudhir

      Arief, I am not sure I understand the question , are you asking if could use the script to add multi-writer disks/flags to new VM ‘s who would be part of the cluster?

  3. Sudhir

    A sincere request, Please do not post Non-Oracle on vSphere related material on this blog post.

    Thanks in advance

  4. Hollie

    That’s before the Sharks woke up in the next period to score two goals and force overtime.
    Another of the first good movies to come from 2007.
    It’s centered on Cornelius Ryan’s tale of Dday (June 6, 1944).

  5. watch black sails online

    You will just need three factors, that’s — personal computer/laptop, internet connection, and internet TV application.

    To plan ahead for that, the Yankees have released C.C. This
    picture provides a fantastic possibility to churches.

  6. cydia tweaks

    The Evo 4G has Android, which indicates it’s technically more “free” than
    the Iphone. Of all the profits when you Jailbreak ipad, this one is the coolest.

    You will require the IMEI for doing all this.

  7. Pingback: » Gotcha Adding Disk to Virtual Oracle RAC Cluster with VMware multi-writer flag Long White Virtual Clouds

  8. Jai Pandurangi


    Can you share the best practice to setup a ORACLE RAC using RDMs and also any other settings required to be added to the vmx file ?

    The above query is with respect to VSphere 5.5

  9. Pingback: Oracle on VMware Collateral - One Stop Shop - Virtualize Business Critical Applications - VMware Blogs

Leave a Reply

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