By default, virtual machines don’t support Hot Add (add RAM) and Hot Plug (add vCPU). You need to enable this capability on a per-VM basis in order to use it. To do so, you must first shut down the virtual machine since you can’t modify these settings while it’s running. Then, open the virtual machine’s properties, navigate to the Options tab and choose the Memory/CPU Hotplug option in the Advanced section. At the right-hand side of the window, note that there are two section – one for memory and one for CPU. Choose the options you like and then click OK. After this setting is changed, you can restart the VM.
Now, when you look at the VM details, notice that you’re provided with the maximum hot-add memory for the VM. In this case, that’s 64 GB.
When I look at the system properties for the VM, here’s what I see: 4 GB of RAM and 2 processors.
While the VM is running, I’m going to increase this to 6 GB of RAM and 3 processors.
Without a reboot, here is what I now see in the system properties.
And he’s a look at the Task Manager showing 3 CPUs and 6 GB of RAM
If you’ve successfully hot added RAM or CPU to a running virtual machine, respond to this posting (or, leave a response to my forum posting) with your operating system, edition (standard, enterprise, etc), service pack level/kernel version, and architecture (32/64-bit). If enough people respond, I’ll compile all of the results into a usable format and republish it.
$VMHost = Get-VMHost 'Server01' | Get-View $VMHost.Hardware.BiosInfo
This will give you results along the lines:
BiosVersion ReleaseDate DynamicType DynamicProperty
———– ———– ———– —————
2.5.0 12/09/2008 00:00:00
What is VMware HA?
As per VMware Definition,
VMware® High Availability (HA) provides easy to use, cost effective high availability for applications running in virtual machines. In the event of server failure, affected virtual machines are automatically restarted on other production servers with spare capacity
What is AAM in HA?
AAM is the Legato automated availability management. Prior to vSphere 4.1, VMware’s HA is actually re engineered to work with VM’s with the help of Legato’s Automated Availability Manager (AAM) software. VMware’s vCenter agent (vpxa) interfaces with the VMware HA agent which acts as an intermediary to the AAM software. From vSphere 5.0, it uses an agent called “FDM” (Fault Domain Manager).
What are pre-requites for HA to work?
1.Shared storage for the VMs running in HA cluster
2.Essentials plus, standard, Advanced, Enterprise and Enterprise Plus Licensing
3.Create VMHA enabled Cluster
4.Management network redundancy to avoid frequent isolation response in case of temporary network issues (preferred not a requirement)
What is maximum number of primary HA hosts in vSphere 4.1?
Maximum number of primary HA host is 5. VMware HA cluster chooses the first 5 hosts that joins the cluster as primary nodes and all others hosts are automatically selected as secondary nodes.
How to see the list of Primary nodes in HA cluster?
View the log file named “aam_config_util_listnodes.log” under /var/log/vmware/aam using the below command
What is the command to restart /Start/Stop HA agent in the ESX host?
service vmware–aam restart
service vmware–aam stop
service vmware–aam start
Where to located HA related logs in case of troubleshooting?
What the basic troubleshooting steps in case of HA agent install failed on hosts in HA cluster?
Below steps are are taken from my blog posts Troubleshooting HA
1. Check for some network issues
2. Check the DNS is configured properly
3. Check the vmware HA agent status in ESX host by using below commands
service vmware–aam status
4. Check the networks are properly configured and named exactly as other hosts in the cluster. otherwise, you will get the below errors while installing or reconfiguring HA agent.
5. Check HA related ports are open in firewall to allow for the communication
Incoming port: TCP/UDP 8042-8045
Outgoing port: TCP/UDP 2050-2250
6. First try to restart /stop/start the vmware HA agent on the affected host using the below commands. In addition u can also try to restart vpxa and management agent in the Host.
service vmware–aam restart
service vmware–aam stop
service vmware–aam start
7. Right Click the affected host and click on “Reconfigure for VMWare HA” to re-install the HA agent that particular host.
8. Remove the affected host from the cluster. Removing ESX host from the cluster will not be allowed untill that host is put into maintenance mode.
9.Alternative solution for 3 step is, Goto cluster settings and uncheck the vmware HA in to turnoff the HA in that cluster and re-enable the vmware HA to get the agent installed.
10. For further troubleshooting , review the HA logs under /Var/log/vmware/aam directory.
What is the maximum number of hosts per HA cluster?
Maximum number of hosts in the HA cluster is 32
What is Host Isolation?
VMware HA has a mechanism to detect a host is isolated from rest of hosts in the cluster. When the ESX host loses its ability to exchange heartbeat via management network between the other hosts in the HA cluster, that ESX host will be considered as a Isolated.
How Host Isolation is detected?
In HA cluster, ESX hosts uses heartbeats to communicate among other hosts in the cluster.By default, Heartbeat will be sent every 1 second.
If a ESX host in the cluster didn’t received heartbeat for for 13 seconds from any other hosts in the cluster, The host considered it as isolated and host will ping the configured isolation address(default gateway by default). If the ping fails, VMware HA will execute the Host isolation response
What are the different types isolation response available in HA?
Power off – All the VMs are powered off , when the HA detects that the network isolation occurs
Shut down – All VMs running on that host are shut down with the help of VMware Tools, when the HA detects that the network isolation occurs.If the shutdown via VMWare tools not happened within 5 minutes, VM’s power off operation will be executed. This behavior can be changed with the help of HA advanced options. Please refer my Post on HA Advanced configuration
Leave powered on – The VM’s state remain powered on or remain unchanged, when the HA detects that the network isolation occurs.
How to add additional isolation address for redundancy?
By default, VMWare HA use to ping default gateway as the isolation address if it stops receiving heartbeat.We can add an additional values in case if we are using redundant service console both belongs to different subnet.Let’s say we can add the default gateway of SC1 as first value and gateway of SC2 as the additional one using the below value
1. Right Click your HA cluster
2. Goto to advanced options of HA
3. Add the line “das.isolationaddress1 = 192.168.0.1″
4. Add the line “das.isolationaddress2 = 192.168.1.1″ as the additional isolation address
To know more about the Advanced HA Options
What is HA Admission control?
As per “VMware Availability Guide”,
VCenter Server uses admission control to ensure that sufficient resources are available in a cluster to provide failover protection and to ensure that virtual machine resource reservations are respected.
What are the 2 types of settings available for admission control?
Enable: Do not power on VMs that violate availability constraints
Disable: Power on VMs that violate availability constraints
What are the different types of Admission control policy available with VMware HA?
There are 3 different types of Admission control policy available.
Host failures cluster tolerates
Percentage of cluster resources reserved as fail over spare capacity
Specify a fail over host
How the Host Failures cluster tolerates admission control policy works?
Select the maximum number of host failures that you can afford for or to guarantee fail over. Prior vSphere 4.1, Minimum is 1 and the maximum is 4.
In the Host Failures cluster tolerates admission control policy , we can define the specific number of hosts that can fail in the cluster and also it ensures that the sufficient resources remain to fail over all the virtual machines from that failed hosts to the other hosts in cluster. VMware High Availability(HA) uses a mechanism called slots to calculate both the available and required resources in the cluster for a failing over virtual machines from a failed host to other hosts in the cluster.
What is SLOT?
As per VMWare’s Definition,
“A slot is a logical representation of the memory and CPU resources that satisfy the requirements for any powered-on virtual machine in the cluster.”
If you have configured reservations at VM level, It influence the HA slot calculation. Highest memory reservation and highest CPU reservation of the VM in your cluster determines the slot size for the cluster.
How the HA Slots are Calculated?
I have written a post about how the HA slots are calculated.
How to Check the HA Slot information from vSphere Client?
Click on Cluster Summary Tab and Click on “Advanced Runtime Info” to see the the detailed HA slots information.
What is use of Host Monitoring status in HA cluster?
Let’s take an example, you are performing network maintenance activity on your switches which connects your one of th ESX host in HA cluster.
what will happen if the switch connected to the ESX host in HA cluster is down?
It will not receive heartbeat and also ping to the isolation address also failed. so, host will think itself as isolated and HA will initiate the reboot of virtual machines on the host to other hosts in the cluster. Why do you need this unwanted situation while performing scheduled maintenance window.
To avoid the above situation when performing scheduled activity which may cause ESX host to isolate, remove the check box in ” Enable Host Monitoring” until you are done with the network maintenance activity.
How to Manually define the HA Slot size?
By default, HA slot size is determined by the Virtual machine Highest CPU and memory reservation. If no reservation is specified at the VM level, default slot size of 256 MHZ for CPU and 0 MB + memory overhead for RAM will be taken as slot size. We can control the HA slot size manually by using the following values.
There are 4 options we can configure at HA advanced options related to slot size
das.slotMemInMB – Maximum Bound value for HA memory slot size
das.slotCpuInMHz – Maximum Bound value for HA CPU slot Size
das.vmMemoryMinMB – Minimum Bound value for HA memory slot size
das.vmCpuMinMHz – Minimum Bound value for HA CPU slot size
For More HA related Advanced options, Please refer my blog post
How the “Percentage of cluster resources reserved as failover spare capacity” admission control policy works?
In the Percentage of cluster resources reserved as failover spare capacity admission control policy, We can define the specific percentage of total cluster resources are reserved for failover.In contrast to the “Host Failures cluster tolerates admission control policy”, It will not use slots. Instead This policy calculates the in the way below
1.It calculates the Total resource requirement for all Powered-on Virtual Machines in the cluster and also calculates the total resource available in host for virtual machines.
2.It calculates the current CPU and Memory Failover capacity for the capacity.
3.If the current CPU and Memory Failover capacity for the cluster < configured failover capacity (ex 25 %)
4.Admission control will not allow to power on the virtual machine which violates the availability constraints.
How the “Specify a failover host” admission control policy works?
In the Specify a failover host” admission control policy, We can define a specific host as a dedicated failover host. When isolation response is detected, HA attempts to restart the virtual machines on the specified failover host.In this Approach, dedicated failover hist will be sitting idle without actively involving or not participating in DRS load balancing.DRS will not migrate or power on placement of virtual machines on the defined failover host.
What is VM Monitoring status?
HA will usually monitors ESX hosts and reboot the virtual machine in the failed hosts in the other host in the cluster in case of host isolation but i need the HA to monitors for Virtual machine failures also. here the feature called VM monitoring status as part of HA settings.VM monitoring restarts the virtual machine if the vmware tools heartbeat didn’t received with the specified time using Monitoring sensitivity.
If you are looking for more VMware interview questions Please click Interview Questions.
Thanks For Reading!!! All the Best…
vSphere HA is an high availability solution from VMware which enables reduction of down time on virtual machines. vSphere High Availability provides availability at virtual machine level, Guest operating system and applications.
High availability is achieved in different ways for various components of virtual infrastructure:
1.Networking : NIC Teaming, Multiple Kernel port groups
3.Viratual Machines : Vmotion, High Availability, FT
vSphere HA leverages multiple Esxi Hosts configured as a cluster to provide rapid recovery from outages and cost effective high Availability for applications running in virtual machines.
vSphere High Availability protects application availability in the following ways:
Advantages of using vmware High Availability over traditional failover solutions:
1. Requirements for enable High Availability:
Types of heart beating used to with High Availability
2. Working of High Availability
Once we enable vmware High Availability on the cluster, the hosts which are part of the cluster and virtual machines on them are protected by High Availability.once hosts added one of the hosts is elected as master hosts and rest as slaves, master hosts, monitors other slave hosts and virtual machines and in case of any network issue, virtual machines guest operating system issues, the virtual machines are either moved to another hosts or restated respectively.
Host with highest number of data stores is elected as master, Master host has the below roles and responsibilities.
If a master host is unable to communicate directly with the agent on a slave host, the slave host does not respond to ICMP pings, and the agent is not issuing Heartbeats it is considered to have failed. The host’s virtual machines are restarted on alternate hosts.If such a slave host is exchanging heartbeats with a datastore, the master host assumes that it is in a network partition or network isolated and so continues to monitor the host and its virtual machines.
Once HA is enabled, in the selected datastores, an auto generated file is created with list of protected virtual machines (powered on Virtual machines in High Availability enabled cluster), so that master hosts knows which virtual machines needs to be restated /migrated when High Availability triggers.
3. Types of host Failures:
There are 3 types of host failures They are:
The master host monitors the liveness of the slave hosts in the cluster. This communication is done through the exchange of network heartbeats every second. when the master host stops receiving these heartbeats from a slave host, it checks for host liveness before declaring the host to have failed. The liveness check that the master host performs is to determine whether the slave host is exchanging heartbeats with one of the datastores. Also, the master host checks weather the host responds to ICMP pings sent to its management IP addresses.
If master host is unable to communicate directly with the agent on a slave host, the slave host does not respond to ICMP pings, and the agent is not issuing heartbeats it is considered to have failed. The host’s virtual machines are restarted on alternate hosts. If such a slave host is exchanging heartbeats with a datastore, the master assumes that it is in a network partition or network isolated and so continues to monitor the host and its virtual machines.
Host Network isolation occurs when a host is still running, but it can no longer observe traffic from vSphere High Availability agents on the management network. If a host stops observing this traffic, it attempts to ping the cluster isolation addresses. If this also fails, the host declares itself as isolated from the network.
The master host monitors the virtual machines that are running on an isolated host and if it observes that they power off, and the master host is responsible for the virtual machines, it restart them.