VMware Interview Questions

• VMware Interview Questions

Explain what is hypervisor
A hypervisor is a program that enables multiple operating systems to share a single hardware host.
The hypervisor controls the resources and host processor, allocating what is required for each operating system in turn and make sure that the guest operating system cannot disrupt each other.

Explain VMware DRS?
VMware DRS stands for Distributed Resource Scheduler; it dynamically balances resources across various host under a cluster or resource pool.

Define the term ’VMKenel’.
VMWare Kernel is a proprietary kernel of VMware. It needs an operating system to boot and manage the kernel. A service console is being offered whenever VMWare kernel is booted.

 What is the use of Promiscuous Mode?
Promiscuous mode is useful when you want to run a virtual machine with network sniffers helps you to capture packet of that network. Moreover, if the promiscuous mode set to accept, all the communication is visible to all the virtual machines.

What is Cold and Hot Migration?
When you migrate powered off or suspended, it is known as cold migration. When you migrate your running power on virtual machines, it is known as hot migration.

What is Virtual Desktop Infrastructure?
Virtual Desktop Infrastructure which also known as VDI allows you to host the desktop operating system on the centralized window server in a data center. It is also known as server-based computing as it is the variation on the client-server computing model.

Explain the importance of snapshot in VMWare
A VMWare snapshot is a copy of a virtual machine disk file which is used to restore a VM to a specific point in time when the system fails, or system error occurs.

What is VVol?
Virtual Volume known as VVol is a new VM disk management feature concept introduced in vSphere 6.0. It enables array-based operation at the virtual disk level.  It is automatically created when a virtual disk is created in a virtual environment.

Can we do vMotion between two data centers?
Yes, we can do vMotion between two datacenters. However,  for this VM should be powered off.

What is RDM?
RDM is a sort form of Raw Device Mapping. It is a file stored in VMFS volume which acts as a proxy for a raw physical device. It allows you to store virtual machine data directly on LUN.

What is NFS?
NFS is a Network file system. It is a file sharing protocol which ESXI host used to communicate with the NAS device. It is a specialized store device which connects to a network and can provide file aces service to ESXI hosts.

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• Explain what happens to a Virtual Machine after the host which it is running on, fails.

First, you should explain that the VM is forcefully powered off.
Next, ask if the host was in a correctly configured HA cluster (If it isn’t then nothing else happens to the VM)
If the Host is HA enabled, then ask what the Virtual Machine restart policy is. If it’s disabled then the VM will not be restarted on other hosts.
Ignoring the HA master election process, the simple answer is that the Virtual Machine will be rebooted on another ESXi host in the cluster.
Mention that there are things that will stop a Virtual Machine from being restarted on other hosts such as Admission Control settings & resource availability on the host.
The key thing to remember is that HA does NOT trigger a vMotion.

When should Promiscuous Mode be enabled on a Virtual Switch

Promiscuous Mode is a vSwitch and Portgroup setting that allows for Virtual Machines to receive all traffic within the same vSwitch or Portgoup (depending on where you set the configuration)
Typical use cases for this are packet sniffing applications.

Name 3 benefits of installing VMware Tools on Virtual Machines

Enables features such as Guest Introspection for NSX / agentless antivirus
Installs the VMXNET3 driver for improved network performance.
Allows the ability to copy and paste between the VM and desktop (some other settings might need to be enabled first)

What techniques are available to ESXi to reclaim memory?

Transparent Page Sharing (TPS) – Note that as of vSphere 6.0, this is disabled by default.
Ballooning – Requests VMware tools to “inflate a memory balloon” inside the VM until excess memory is released back to ESXi.
Memory Compression.
Swapping – This is the last option that ESXi will use to reclaim memory because it is the most disruptive to performance as memory gets swapped out from real memory onto disk

What is the impact of using Thick Eager Zeroed disk provisioning for VMDKs?
This disk type will zero out all data on the disk before allocating the VMDK to the Virtual Machine.
This has some performance benefit to the VM because it doesn’t have to zero a block before it can be written to.
The negative side is that it takes longer to provision the VMDK to the VM (since it has to zero all blocks first) and it has a measurable, sustained IO hit on the storage system

What are the main benefits of a Distributed Switch?
    Central Management of all ESXi host’s networking, meaning that there is only one switch to manage rather than one per host.
    The ability to enable Network IO Control (NIOC)
    NetFlow support.

Name 3 Virtual Machine Files

    VMX – The Virtual Machine configuration file
    NVRAM – The VM’s BIOS file
    VMEM – The VM’s pagefile
    VMSD – VM Snapshot state file


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