Virtualization is the answer to easy application deployment, maximum server utilization, and robust disaster recovery plans. To cater to this rising deployment of virtualization around the globe, VMware administrators are in great demand. VMware is the leading virtualization platform on market with vSphere product and it is a great career if you have choosen this and all about VMware products.
In this article, starting from my previous experience with interviews, I’ll show some of the common VMware interview questions and asnwer for them, for helping you in your further interviews.
- What is hypervisor?
Hypervisor is a program that enables multiple operating systems to share a single hardware host. Each operating system has the host’s processor, memory and other resources all to itself. 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.
- What is VMware DRS?
VMware DRS stands for Distributed Resource Scheduler; it dynamically balances resources across various host under cluster or resource pool. It enables users to determine the rules and policies which decide how virtual machines deploy resources, and these resources should be prioritized to multiple virtual machines.
- What is a Template?
We can convert a VM into Template, and it cannot be powered on once its changed to template. This is used to quick provisioning of VM’s. A template is a master copy of a virtual machine; it can be used to make many clones. Template can be converted back to the virtual machine to update the base template.
- Why snapshots are really important in VMWare?
Snapshots are images that is been taken at a particular point from the virtual guest operating system. The snapshot consists of the virtual machine configurations, memory and the devices that were present at the time of the snapshot. By doing this, you can return back to virtual machine which might have become corrupted or might not be working. Snapshots can be saved and then system can be reverted back in case of any disaster happened to your operating system.
- What is the role of VMware vCenter server?
vCenter provides a centralized management platform and framework for all ESXi hosts and their respective VMs. vCenter server allows IT administrators to deploy, manage, monitor, automate, and secure a virtual infrastructure in a centralized fashion.
- What is vCenter Agent?
VC agent is an agent installed on ESX server which enables communication between VC and ESX server. The daemon associated with it is called vmware-hostd , and the service which corresponds to it is called as mgmt-vmware, in the event of VC agent failure just restart the service.
- What is VMKernel?
VMkernel is an interface between VMs and the VMware ESX host. Its main function is to allocate memory, to schedule the CPUs and is necessary to run many of the services like vMotion, Fault tolerance, NFS, traffic management and iSCSI. VMkernel port can be configured on ESX server using a standard vSwitch . VMWare Kernel is a Proprietary Kenral and is not based on any of the UNIX operating systems, it’s a kernel developed by VMware Company.
- What is the impact on HA,DRS, and FT if vCentre is down?
-High availability is managed by HA agent which is installed on vCenter server while configuring hosts. So even if vCenter Server is not working, HA will keep on working since HA is controlled by FDM agents.
-DRS. In case vCenter is down, DRS will stop working since the distribution of VMs is a function of vCenter Server.
-Although you will not be able to create VMs, the already configured VMs will not be affected in case of vCenter outage.
- What is Virtual Switch in VMware and how many type are?
Switches are used to establish a connection between the virtual network and the physical network. With ESX and ESXi, two different kinds of switches can be used:
-Standard Switches – A network standard switch, virtual switch, or vSwitch, is responsible for connecting virtual machines to a virtual network. A vSwitch works similar to a physical switch and controls how virtual machines communicate with one another.
-Distributed Switches — Distributed virtual switches, or DvSwitches, simplify the network management of multiple ESX or ESXi hosts. DvSwitches provide the same features and functions as do vSwitches, but with one major difference: while a standard virtual switch can’t be assigned to more than one host server at a time, a DvSwitch can. So, rather than create identical vSwitches for multiple hosts in a datacenter, you can instead create and associate a single DvSwitch with all the applicable ESX or ESXi servers.
- What is vMotion? Can we do vMotion between vCenters?
VMware vMotion enable live migration of virtual machines among various physical servers, while the VMs are running, with no downtime, no interruption in service, and total transaction integrity. VMotion improves the availability of VMs by enabling maintenance without incurring disruption to the business operations. It moves VMs within pools of server resources so that resources are allocated according to the priorities of the business.
Yes we can do vMotion between two datacenters, but our environment must meet some requirements :
-The cross vCenter Server and long distance vMotion features require an Enterprise Plus license.
-When using the vSphere Web Client, both vCenter Server instances must be in Enhanced Linked Mode and must be in the same vCenter Single Sign-On domain.
-Both vCenter Server instances must be time-synchronized with each other.
-Both vCenter Server instances must be connected to the shared virtual machine storage.
- What are the three port groups present in ESX server networking?
-Virtual Machine Port Group – Used for Virtual Machine Network
-Service Console Port Group – Used for Service Console Communications
-VMKernel Port Group – Used for VMotion, iSCSI, NFS Communication.
- What are the types for Network Failover Detection settings?
Network failover detection is a mechanism used to detect a network failure. Two network failover detection methods are available in vSphere when using a standard virtual switch:
-Link status only– relies on the link status provided by the network adapter. This method can detect failures like cable pulls and physical switch power failures, but can not detect configuration errors. This is the default.
-Beacon probing– probes are sent out and listened for on all NICs in the team. This method can determine link status and failures that the Link status only method can not, such as configuration errors and cable pulls on the other side of a physical switch. Beacon probing should not be used in conjunction with the IP Hash load-balancing policy.
- What is a datastore and LUN?
Datastore is a manageable storage entity, logical containers usually used as a repository for virtual machine files including log files, scripts, configuration files, virtual disks, and so on. vSphere supports two types of datastores, VMFS and NAS.
A LUN (Logical Unit Number) is an identifier for a disk volume in a storage array target. LUN is a piece of your SAN, logical unit created from disk arrays. From a LUN you can create as many datastores as you want, that are presented to hosts in vsphere client. We can also connect multiple LUNs to create a single large datastore.
- What happens to vSAN when vCenter Server is offline?
The answer is: Nothing. vSAN continues to operate normally and virtual machines continue to run. When vCenter Server is offline, the main disadvantage is we lose the full-featured functionality of the vSphere Web Client until vCenter Server is back online. With vSAN 6.6 and newer versions, we can point a web browser directly at the ESXi management IP or FQDN of any host in the vSAN cluster and log in to the vSphere Host Client to monitor vSAN.
- What is VMware HA (High Availability) and how does it work?
VMware HA provides high availability for virtual machines by pooling them and the hosts they reside on into a cluster. Hosts in the cluster are monitored and in the event of a failure, the virtual machines on a failed host are restarted on alternate hosts.
VMware HA only works if VM files are retained on shared storage, such as a SAN. All hosts in the cluster are capable of accessing VM files on this shared storage and restarting the VM.
Hosts in the cluster communicate via a VMware HA utility, which maintains and monitors each host’s heartbeat — a periodic message that indicates the host is still running. If the host stops transmitting its heartbeat communication, because of a failure for example, other hosts in the cluster will recognize its absence and restart the VMs on remaining hosts.