Advanced Configuration options for VMware HA

In this post I am going to cover a few advance settings in HA which you can be used in deploying complex HA solutions. You may or may not be using these advance value in your environment but sometimes you have to use these values depending upon how your virtualization infrastructure is laid.

1: das.isolationaddress: – By default the IP address used to check host isolation is the default gateway of the VMkernel port on the host. You can add more IP addresses for the host to use during an isolation check. A total of 10 addresses can be used (0-9).

For setting up this value Select Cluster > Edit Settings > vSphere HA > Advanced Options



2: das.usedefaultisolationaddress:– this option has 2 values: True or False. When set to false a host will NOT use the default gateway as an isolation address. This may be useful when the default gateway of your host is an unpingable address, or a virtual machine, such as a virtual firewall


3: das.isolationShutdownTimeout:– use this option to specify the amount of time (in seconds) it will wait for a guest shutdown process that was initiating by invoking the isolation response, before HA will forcefully power off a virtual machine.

4: das.heartbeatDsPerHost:— set this to the number heartbeat datastores you want to use. If you have a need to configure more than two heartbeat datastores per host you can used this advanced setting. The value range of this setting is 2-5.

Create a custom slot size configuration

By default HA will take the largest CPU and memory reservation of virtual machines in a cluster to determine Slot size for the cluster/hosts. But we can force HA to use user defined value of CPU and memory to calculate slot size. There are two advanced settings that you can configure in order to create a custom slot size; one for CPU and one for memory

das.slotCpuInMHz : The value of CPU slot size in MHz.

das.slotMemInMB : Value of memory slot size in MB.

These advanced setting “das.slotCpuInMHz “and “das.slotMemInMB” allow you to specify an upper boundary for your slot size. If you have large reservations set on only a few VM’s it can cause setting large slot size and will waste resources in your cluster as most of your VM’s will be running without any reservation.

For e.g: When one of your VMs has an 8GB reservation this setting can be used to define for instance an upper boundary of 1 GB to avoid resource wastage and an overly conservative slot size.

Important Note: If the highest CPU and memory reservation is below the value as specified in advance settings, then HA will take the value which is minimum.


5 das.ignoreinsufficienthbdatastore:– Disables configuration issues created if the host does not have sufficient heartbeat datastores for vSphere HA. Default value is false.

6: das.vmCpuMinMHz:– Min amount of CPU that is guaranteed to a VM when that VM is failed over (restarted) after a host failure. If CPU reservation is set on a VM then this value wont work for that VM, but will work for those VM’s which have 0 MHz reservation set.

7 :das.vmMemoryMinMB:- Min amount of memory that is guaranteed to a VM when that VM is failed over (restarted) after a host failure. If Memory reservation is set on a VM then this value wont work for that VM, but will work for those VM’s which have 0 MB  reservation set.

The above 2 values are used with “Percentage Based Admission Control”


About Manish Jha

Hi All I am Manish Kumar Jha aka Alex Hunt. I am currently working in VMware Software India Pvt Ltd as Operations System Engineer (vCloud Air Operations). I have around 5 Years of IT experience and have exposure on VMware vSphere, vCloud Director, RHEL and modern data center technologies like Cisco UCS and Cisco Nexus 1000v and NSX. If you find any post informational to you please press like and share it across social media and leave your comments if you want to discuss further on any post. Disclaimer: All the information on this website is published in good faith and for general information purpose only. I don’t make any warranties about the completeness, reliability and accuracy of this information. Any action you take upon the information you find on this blog is strictly at your own risk. The Views and opinions published on this blog are my own and not the opinions of my employer or any of the vendors of the product discussed.
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