Home > Uncategorized > Increase Number of VMware HA Primaries – How To?

Increase Number of VMware HA Primaries – How To?


A bit of history, the first five hosts added to an VMware HA cluster are designated as primary hosts, and all subsequent hosts are designated as secondary hosts. The primary hosts maintain and replicate all cluster state and are used to initiate failover actions. At least one primary host must be functional for VMware HA to operate correctly. If all primary hosts are unavailable (not responding), no hosts can be successfully configured for VMware HA. One of the primary hosts is also designated as the active primary host and if it fails, another primary host replaces it in that role.

The researches I’ve made for my previous post about VMware HA (VMware HA – Lack and Limitation) led to a file within /opt/vmware/aam/ha/ directory.
The file over there is called VMWareConfig.def and contains some of the very fundamental and enhanced functions, routines and variables of VMware HA. One particular variable caught my attention:

name = MAX_PRIMARY_COUNT
value = 5

I know for some times now that the limitation to 5 primary nodes in a VMware HA cluster was a software limitation. Up to last week I didn’t know where that VMware HA limit was set.
Unfortunately I don’t have enough ESX hosts in my home lab to test my finding and therefore I rely on the community to help me here test my theory.

Reminder: this is an UNSUPPORTED hack that can lead to UNSTABLE system! Don’t try this on a production environment (don’t even think about it) and read the disclaimer below! I shall not be liable for any damages arising out! Now that I have scared you let’s dig in the theory.

There might be several items to change within VMWareConfig.def:
- First item
name = MAX_PRIMARY_COUNT
value = 5 -> change to 6 or higher number!

- Second item
if ($ft::RunCount == 1) {
$MAX_PRIMARY_COUNT=5; -> Does it need to changed as well?? Not sure!

My guess only the first item needs to be changed, it’s kinda of global variables. The second item is kinda of subroutine to check if the global variable has been changed or not.
You need to change the value(s) to all ESX(i) hosts participating to your VMware HA cluster. Also you certainly need to restart the aam service to take the new value(s) into account:
-For ESXi: /sbin/services.sh restart
-For ESX:  services vmware-aam restart

To see the number of primaries, 2 methods:

  1. From the Service Console:
  2. cat /var/log/vmware/aam/aam_config_util_listnodes.log

  3. From AAM’s cli:
  4. /opt/vmware/aam/bin # ./Cli -cmd ln

Feedback and comments are welcome, thanks!

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  1. March 26, 2010 at 15:43 | #1

    Hello Didier,

    Nice post. As I understand you didn’t test this?

    A colleauge of mine tested this and you can set the max number of primaries higher then 6 but effectively no more then 6 hosts become primary, the rest stays secondary.

    • deinoscloud
      March 26, 2010 at 16:12 | #2

      Hi Matthijs, thx for commenting. So no matter what value you put there, 6 primaries is the maximum you can get as I understand you… Wondering where is the other ‘lock’ to get more primaries than 6 :)

  2. March 28, 2010 at 09:12 | #3

    I would just like to note that there’s a really good reason for VMware to pick the max 5 primaries, PLEASE don’t change this value. If you run into issues you will not get any support.

  3. April 1, 2010 at 18:32 | #4

    BTW, i bet this setting will go away in case of “Reconfigure for VMware HA” call

  1. March 26, 2010 at 15:37 | #1
  2. April 17, 2010 at 18:07 | #2

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