vMotion Interview Questions

This Post is all about the vMotion. I hope I have covered the things like the definition of the vMotion, requirements for configuring the vMotion, failure scenario’s, things to look for troubleshooting the vMotion. Above all I did it in Questions and Answers style. I hope you like it.


What is vMotion?


VMotion is the technology that VMware uses to migrate the Powered ON virtual machine from one ESX/ESXi server to the other ESX/ESXi server without disrupting the running services and without any downtime. VMware DRS also uses vMotion to automatically load balance the resources across the ESX hosts in a cluster.

vMotion would be helpful when we want to perform the Maintenance of the ESX Server, which makes sure that the ESX maintenance will not impact any Virtual Machines.

What exactly happens when the vMotion is initiated?


When the Virtual Machine migration is initiated using the Migrate option,  the entire state of the virtual machine is being moved from one ESXi Server to the other ESXi Server while the making the data and associated files remains at the same datastore where the Virtual Machine is running.

The definition and identification information stored in the state includes all the data that maps to the virtual machine hardware elements, such as: such as BIOS, devices, CPU, MAC addresses for the Ethernet cards.

What are the different uses of vMotioin?

  • VMware uses vMotion to migrate the virtual machine from one ESX to the other ESX Server without any downtime. This would be helpful if you want to perform any hardware Maintenance on the ESX Servers.
  • DRS also uses Motion to perform the load balancing across all the ESX Servers in the cluster.

What are the requirements for configuring the vMotion?

  •  License – The hosts must be licensed for vMotion.
  • Processor compatibility – you need to have the common processors in the ESX/ESXi servers and there shouldn’t be any affinity rules defined on the virtual machine.
  • Network – Atleat Gigabit Ethernet card on the ESX Host.
  • Storage– Common storage configured on the destination ESX/ESXi servers.
  • vMotion Must be enabled– You need to have the VMkernel Portgroup enabled for vMotion.
  • If there is any RDM configured on the virtual machine then the destination ESX servers must also need to have access to the RDM.
  • Virtual machines with USB passthrough devices can be migrated with vMotion as long as the devices are enabled for vMotion.
  • Virtual machine must be connected to the virtual switch

How many Virtual Machine Migrations can be done at once?

  • Each VMFS datastore can support up to 128 concurrent vMotion migrations.
  • Up to four concurrent vMotion migrations are supported on a 1Gbps vMotion network.
  • Up to eight concurrent vMotion migrations are supported on a 10Gbps network.

How vMotion Migration Works?


Here are the few steps that were involved during vMotion Migration process.
  • When the vMotion Migration is initiated the virtual Machine’s memory is being copied from the source ESX/ESXi Server to the destination ESX/ESXi Server over the vMotion Network. The users will continue to have the access to the virtual machine, and the users updated memory pages would be stored in a bitmap image.
  • Once the active memory pages are being copied to the destination that the virtual machine will be quiesced for a couple of seconds to copy the bitmap image to the destination ESX/ESXi server.
  • When the virtual machine is quiesced and the bitmap image is copied to the destination ESX/ESXi, the virtual machine continues to run on the destination host.
  • The RARP notifies the subnet that the Virtual Machine MAC address has been connected to the new switch port.
  • Once the bitmap image is copied from the source to the destination ESXi host, the memory pages at the source ESXi would be freed.

In what scenarios that the vMotion will fail?


  • When the ESX servers processor not matching, then vmotion will fail
  • When you dont have the Common storage
  • When you doont have the vmkernel enabled for vmotion.
  • When you have any external devices mapped to the Virtual Machine.
  • When you have the Physical RDM mapped to the virtual machine.
  • When the virtual machine is running on Local Storage
  • Fault Taulernance VMs cant be migrated in cluster of only two nodes.
  • vMotion will fail if there was DRS rule created to not to vMotion the Virtual Machine.
  • vMotion feature is not available with Essential Licensing.
  • Fails if the Swap file is not accessible by the destination ESXi host.
  • ESX Server Network card duplex setting might impact.

 How do you proceed troubleshooting the vMotion issues?

Here are the few things that you have to verify for the vMotion failures.

  • If the vMotion network is not configured or functioning properly, vMotion migrations can fail.
  • The ESXi host must be configured properly and should have sufficient resources to allow virtual machine migrations from one ESXi Host to the other ESXi Host.
  • verify the vMotion Network on the VMkernel adapter using the command 

            # ping

  • Verify both the source and destination ESX Servers are resolving the both the names and IP address using

            # nslookup&nslookup

  •  Ensure that the VMkernel interface is enabled for vMotion traffic.
  • Verify the DNS server configured and ensure that it has the correct information for both the source and destination ESX/ESXi Servers
  • Check the NTP settings and verify the time on the source and destination hosts
  • Verify that the virtual machine does not have reservations and ensure that the destination ESX Host has suffiecient resources for the vMotion to succeed.
 
Where do you find Virtual Machine Migration History?
  • Login to the vCenter server using VI Client -> select the Virtual Machine -> click on the Tasks and events Menu. At the tasks and events you will find the history of the Virtual Machine Migrations.
  • Login to the ESX Server using Putty -> in the /proc/vmware/migration/history you can find the history of the virtual machines migrated from the ESX Server.


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