VMWare Interview Questions with Answers

      1. What is a Hypervisor?
  ð  It is a program that allows multiple operating systems to share a single hardware host. Each     operating system appears to have the host's processor, memory, and other resources all to itself. However, the hypervisor is actually controlling the host processor and resources, allocating what are needed to each operating system in turn and making sure that the guest operating systems (called virtual machines) cannot disrupt each other.

       2. What is the difference between the vSphere ESX and ESXi architectures?
 ð  VMware ESX and ESXi are both bare metal hypervisor architectures that install directly on the server hardware.
Although neither hypervisor architectures relies on an OS for resource management, the vSphere ESX architecture relied on a Linux operating system, called the Console OS (COS) or service console, to perform two management functions: executing scripts and installing third-party agents for hardware monitoring, backup or systems management.
In the vSphere ESXi architecture, the service console has been removed. The smaller code base of vSphere ESXi represents a smaller “attack surface” and less code to patch, improving reliability and security.

      3. What are the files that make a Virtual Machine? 
 ð   .vmx - Virtual Machine Configuration File 
               .nvram - Virtual Machine BIOS 
               .vmdk - Virtual Machine Disk file 
               .vswp - Virtual Machine Swap File 
               .vmsd - Virtual Machine Snapshot Database 
               .vmsn - Virtual Machine Snapshot file 
               .vmss - Virtual Machine Suspended State file 
               .vmware.log - Current Log File 
               .vmware-#.log - Old Log file

       4. What are the three port groups present in ESXi server networking?
 ð    1. Virtual Machine Port Group - Used for Virtual Machine Network
                2. Service Console Port Group - Used for Service Console Communications
                3. VMKernel Port Group - Used for VMotion, iSCSI, NFS Communications

       5. What is the use of a Port Group?
 ð  The port group segregates the type of communication.

       6. What is VMware vMotion and what are its requirements?
 ð  VMware VMotion enables the live migration of running virtual machines from one physical server to another with zero downtime.
VMotion lets you:
“Automatically optimize and allocate entire pools of resources for maximum hardware utilization and Availability.
Perform hardware maintenance without any scheduled downtime.
Proactively migrate virtual machines away from failing or underperforming servers.”

Below are the pre-requisites for configuring vMotion
“Each host must be correctly licensed for vMotion
Each host must meet shared storage requirements
vMotion migrates the vm from one host to another which is only possible with both the host are sharing a common storage or to any storage accessible by both the source and target hosts. 
A shared storage can be on a Fiber Channel storage area network (SAN), or can be implemented using iSCSI SAN and NAS.
If you use vMotion to migrate virtual machines with raw device mapping (RDM) files, make sure to maintain consistent LUN IDs for RDMs across all participating hosts.
Each host must meet the networking requirements
Configure a VMkernel port on each host.
Dedicate at least one GigE adapter for vMotion.
Use at least one 10 GigE adapter if you migrate workloads that have many memory operations.
Use jumbo frames for best vMotion performance.
Ensure that jumbo frames are enabled on all network devices that are on the vMotion path including physical NICs, physical switches and virtual switches.”

        7. What is the difference between Thick provision Lazy Zeroed, Thick provision Eager Zeroed And Thin provision?
 ð  Thick Provision Lazy Zeroed
Creates a virtual disk in a default thick format.
Space required for the virtual disk is allocated when the virtual disk is created.
Data remaining on the physical device is not erased during creation, but is zeroed out on demand at a later time on first write from the virtual machine.
Using the default flat virtual disk format does not zero out or eliminate the possibility of recovering deleted files or restoring old data that might be present on this allocated space.
You cannot convert a flat disk to a thin disk.
     Thick Provision Eager Zeroed
A type of thick virtual disk that supports clustering features such as Fault Tolerance.
Space required for the virtual disk is allocated at creation time.
In contrast to the flat format, the data remaining on the physical device is zeroed out when the virtual disk is created.
It might take much longer to create disks in this format than to create other types of disks.
     Thin Provision
It provides on on-demand allocation of blocks of data.
All the space allocated at the time of creation of virtual disk is not utilized on the hard disk, rather only the size with utilized data is locked and the size increases as the amount of data is increased on the disk.
With thin provisioning, storage capacity utilization efficiency can be automatically driven up towards 100% with very little administrative overhead.

      8. What is a snapshot?
 ð  A snapshot is a “point in time image” of a virtual guest operating system (VM). That snapshot contains an image of the VMs disk, RAM, and devices at the time the snapshot was taken. With the snapshot, you can return the VM to that point in time, whenever you choose. You can take snapshots of your VMs, no matter what guest OS you have and the snapshot functionality can be used for features like performing image level backups of the VMs without ever shutting them down.

       9. What is VMware HA?
 ð  VMware HA i.e. High Availability which works on the host level and is configured on the Cluster.A Cluster configured with HA will migrate and restart all the vms running under any of the host in case of any host-level failure automatically to another host under the same cluster.VMware HA continuously monitors all ESX Server hosts in a cluster and detects failures.VMware HA agent placed on each host maintains a heartbeat with the other hosts in the cluster using the service console network. Each server sends heartbeats to the others servers in the cluster at five-second intervals. If any servers lose heartbeat over three consecutive heartbeat intervals, VMware HA initiates the failover action of restarting all affected virtual machines on other hosts.You can set virtual machine restart priority in case of any host failure depending upon the critical nature of the vm.
     NOTE: Using HA in case of any host failure with RESTART the vms on different host so the vms state will be interrupted and it is not a live migration

      10. What is the difference between VMware HA and vMotion?
 ð  VMware HA is used in the event when any of the hosts inside a cluster fails then all the virtual machines running under it are restarted on different host in the same cluster.Now HA is completely dependent on vMotion to migrate the vms to different host so vMotion is just used for the migration purpose between multiple hosts. vMotion also has the capability to migrate any vm without interrupting its state to any of the host inside cluster.

     11. What is storage vMotion?
 ð  Storage vMotion is similar to vMotion in the sense that "something" related to the VM is moved and there is no downtime to the VM guest and end users. However, with SvMotion the VM Guest stays on the server that it resides on but the virtual disk for that VM is what moves.
With Storage vMotion, you can migrate a virtual machine and its disk files from one datastore to another while the virtual machine is running.
You can choose to place the virtual machine and all its disks in a single location, or select separate locations for the virtual machine configuration file and each virtual disk.
During a migration with Storage vMotion, you can transform virtual disks from Thick-Provisioned Lazy Zeroed or Thick-Provisioned Eager Zeroed to Thin-Provisioned or the reverse.
Perform live migration of virtual machine disk files across any Fiber Channel, iSCSI, FCoE and NFS storage

      12. What is VMware DRS and how does it works?
 ð  Here DRS stand for Distributed Resource Scheduler which dynamically balances resource across various hosts under Cluster or resource pool.
VMware DRS allows users to define the rules and policies that decide how virtual machines share resources and how these resources are prioritized among multiple virtual machines.
Resources are allocated to the virtual machine by either migrating it to another server with more available resources or by making more “space” for it on the same server by migrating other virtual machines to different servers.
The live migration of virtual machines to different physical servers is executed completely transparent to end-users through VMware VMotion
VMware DRS can be configured to operate in either automatic or manual mode. In automatic mode, VMware DRS determines the best possible distribution of virtual machines among different physical servers and automatically migrates virtual machines to the most appropriate physical servers. In manual mode, VMware DRS provides a recommendation for optimal placement of virtual machines, and leaves it to the system administrator to decide whether to make the change.

      13. What is VMware Fault Tolerance?
 ð  VMware Fault Tolerance provides continuous availability to applications running in a virtual machine, preventing downtime and data loss in the event of server failures.
VMware Fault Tolerance, when enabled for a virtual machine, creates a live shadow instance of the primary, running on another physical server.
The two instances are kept in virtual lockstep with each other using VMware vLockstep technology
The two virtual machines play the exact same set of events, because they get the exact same set of inputs at any given time.
The two virtual machines constantly heartbeat against each other and if either virtual machine instance loses the heartbeat, the other takes over immediately. The heartbeats are very frequent, with millisecond intervals, making the failover instantaneous with no loss of data or state.
VMware Fault Tolerance requires a dedicated network connection, separate from the VMware VMotion network, between the two physical servers.

      14. What is promiscuous mode in VMware?
 ð  If the promiscuous mode set to Accept, all the communication is visible to all the virtual machines, in other words all the packets are sent to all the ports on vSwitch
      If the promiscuous mode set to Reject, the packets are sent to intended port, so that the intended Virtual machine was able to see the communication.

       15. Does the vSwitches support VLAN Tagging? Why? 
 ð  Yes, the vSwitches support VLAN Tagging; otherwise if the virtual machines in an esx host are connected to different VLANS, we need to install a separate physical nic (vSwitch) for every VLAN. That is the reason VMware included the VLAN tagging for vSwitches. So every vSwitch supports up to 1016 ports, and BTW they can support 1016 VLANS if needed, but an ESX server doesn’t support that many VM’s. 

      16. What is MAC address Changes? What happens if it is set to Accept?
 ð  When we create a virtual machine the configuration wizard generates a MAC address for that machine, you can see it in the .vmx (VM Config) file. If it doesn't matches with the MAC address in the OS this setting does not allow incoming traffic to the VM. So by setting Reject Option both MAC addresses will be remains same and the incoming traffic will be allowed to the VM.

       17. What is Forged Transmits? What happens if it is set to Accept?
 ð  When we create a virtual machine the configuration wizard generates a MAC address for that machine, you can see it in the .vmx (VM Config) file. If it doesn't matches with the MAC address in the OS this setting does not allow outgoing traffic from the VM. So by setting Reject Option both MAC addresses will be remains same and the outgoing traffic will be allowed from the VM.

4 Responses to “VMWare Interview Questions with Answers”

25 January 2015 at 13:10

Question #9: Default HA Heartbeat interval is 1 Sec.

Failure Detection and Host Network Isolation

Agents communicate with each other and monitor the liveness of the hosts in the cluster. This is done through the exchange of heartbeats, by default, every second. If a 15-second period elapses without the receipt of heartbeats from a host, and the host cannot be pinged, it is declared as failed. In the event of a host failure, the virtual machines running on that host are failed over, that is, restarted on the alternate hosts with the most available unreserved capacity (CPU and memory.)

Prashant Shalgar said...
25 January 2015 at 22:07

Thanks Prakash..

kavaskarg said...
3 February 2015 at 02:50

Simply superb..Keep rocks..

DHAMU G said...
15 March 2016 at 23:25


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