VMWare Interview Questions & Tips

VMkernel

The VMkernel is the liaison between virtual machines (VMs) and the physical hardware that supports them. VMware calls VMkernel a microkernel because it runs on bare metal, directly on VMware ESX hosts. The VMkernal is responsible for allocating memory, scheduling CPUs and providing other hardware abstraction and operating system (OS) services.

VMware resource pool

A VMware resource pool is the aggregated physical compute hardware -- CPU and memory, as well as other components -- allocated to virtual machines (VMs) in a VMware virtual infrastructure. The VMware resource pool manages and optimizes these physical resources for virtual systems within a VMware Distributed Resource Scheduler (DRS) cluster. With memory overcommit, more resources can be allocated to VMs than are physically available. Changes that occur in one resource pool will not affect other, unrelated resource pools VMware administrators create. 

VMware DRS (Distributed Resource Scheduler)

VMware DRS (Distributed Resource Scheduler) is a utility that balances computing workloads with available resources in a virtualized environment. The utility is part of a virtualization suite called VMware Infrastructure 3.
With VMware DRS, users define the rules for allocation of physical resources among virtual machines. The utility can be configured for manual or automatic control. Resource pools can be easily added, removed or reorganized. If desired, resource pools can be isolated between different business units. If the workload on one or more virtual machines drastically changes, VMware DRS redistributes the virtual machines among the physical servers. If the overall workload decreases, some of the physical servers can be temporarily powered-down and the workload consolidated.
Other features of VMware DRS include:

• Dedicated infrastructures for individual business units
• Centralized control of hardware parameters
• Continuous monitoring of hardware utilization
• Optimization of the use of hardware resources as conditions change
• Prioritization of resources according to application importance
• Downtime-free server maintenance
• Optimization of energy efficiency
• Reduction of cooling costs.

VMware Topics Index : 

1. 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.

2. The VMKernel can't boot it by itself, so that it takes the help of the 3rd party operating system. In VMWare case the kernel is booted by RedHat Linux operating system which is known as service console.

3. The service console is developed based up on Redhat Linux Operating system, it is used to manage the VMKernel 

4. To restart webaccess service on vmware 

service vmware-webaccess restart – this will restart apache tomcat app

5. To restart ssh service on vmware

service sshd restart

6. To restart host agent(vmware-hostd) on vmware esx server
service mgmt-vmware restart

7. Path for the struts-config.xml
/usr/lib/vmware/webAccess/tomcat/apache-tomcat-5.5.17/webapps/ui/WEB-INF/

8. To start the scripted install the command is
    esx ks=nfs:111.222.333.444:/data/KS.config ksdevice=eth0
               location                                             device name

9. Virtual Network in Simple……………….

Virtual Nic(s) on Virtual Machine(s) -----> 

Physical Nic on the ESX Server (Virtual Switch - 56 Ports)  ----->

Physical Switch Port              Should be trunked with all the VLANS to which the VM's need access  

All the ESX servers should be configured with Same number of Physical Nics (vSwitches) and Connectivity also should be same, So that vMotion succeeds
All the Virtual Machines are connected to one vSwitch with Different VLANS, this means the Physical Nic(vSwitch) needs to be trunked with the same VLANS on the Physical Switch Port

10 What are the three port groups present in ESX server networking
   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

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

12. What are the type of communications which requires an IP address for sure ?
   Service Console and VMKernel (VMotion and iSCSI), these communications does not happen without an ip address (Whether it is a single or dedicated)

13. In the ESX Server licensing features VMotion License is showing as Not used, why?
    Even though the license box is selected, it shows as "License Not Used" until, you enable the VMotion option for specific vSwitch

14. How the Virtual Machine Port group communication works ?
     All the vm's which are configured in VM Port Group are able to connect to the physical machines on the network. So this port group enables communication between vSwitch and Physical Switch to connect vm's to Physical Machine's

15. What is a VLAN ?
     A VLAN is a logical configuration on the switch port to segment the IP Traffic. For this to happen, the port must be trunked with the correct VLAN ID.

16. Does the vSwitches support VLAN Tagging? Why? 
     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 upto 1016 ports, and BTW they can support 1016 VLANS if needed, but an ESX server doesn’t support that many VM’s. :)  

17. What is Promiscuous Mode on vSwitch ? What happens if it sets to Accept?
     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 inteded port, so that the intended virtual machine was able to see the communication.

18. What is MAC address Changes ? What happens if it is set to Accept ?
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.

19. What is Forged Transmits ? What happens if it is set to Accept ?
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.

20. What are the core services of VC ?
VM provisioning , Task Scheduling and Event Logging

21. Can we do vMotion between two datacenters ? If possible how it will be?
Yes we can do vMotion between two datacenters, but the mandatory requirement is the VM should be powered off.

22. What is VC agent? and what service it is corresponded to? What are the minimum req's for VC agent installation ?
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 by typing the following command at the service console       

     " service mgmt-vmware restart "
VC agent installed on the ESX server when we add it to the VC, so at the time of installtion if you are getting an error like " VC Agent service failed to install ", check the /Opt size whether it is sufficient or not.

23. How can you edit VI Client Settings and VC Server Settings ?
Click Edit Menu on VC and Select Client Settings to change VI settings
Click Administration Menu on VC and Select VC Management Server Configuration to Change VC Settings

24. What are the files that make a Virtual Machine  ?
     .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

25. What are the devices that can be added while the virtual Machine running
In VI 3.5 we can add Hard Disk and NIC's while the machine running.

In vSphere 4.0 we can add Memory and Processor along with HDD and NIC's while the machine running 

26. How to set the time delay for BIOS screen for a Virtual Machine?
Right Click on VM, select edit settings, choose options tab and select boot option, set the delay how much you want.

27. 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.

23. What to do to customize the windows virtual machine clone,?
copy the sysprep files to Virtual center directory on the server, so that the wizard will take the advantage of it.

24. What to do to customize the linux/unix virtual machine clone,?
VC itself includes the customization tools, as these operating systems are available as open source.

25. Does cloning from template happens between two datacenters ?
Yes.. it can, if the template in one datacenter, we can deploy the vm from that template in another datacenter without any problem.

26. What are the common issues with snapshots? What stops from taking a snapshot and how to fix it ?
If you configure the VM with Mapped LUN's, then the snapshot failed. If it is mapped as virtual then we can take a snapshot of it.
If you configure the VM with Mapped LUN's as physical, you need to remove it to take a snapshot.

27. What are the settings that are taken into to consideration when we initiate a snapshot ?
Virtual Machine Configuration (What hardware is attached to it)
State of the Virtual Machine Hard Disk file ( To revert back if needed)
State of the Virtual Machine Memory (if it is powered on)

28. What are the requirements for Converting a Physical machine to VM ?
An agent needs to be installed on the Physical machine
VI client needs to be installed with Converter Plug-in
A server to import/export virtual machines

29. What is VMWare consolidated backup ?
It is a backup framework, that supports 3rd party utilities to take backups of ESX servers and Virtual Machines. Its not a backup service.

30. To open the guided consolidation tool, what are the user requirements ?
The user must be member of administrator, The user should have "Logon as service" privileges - To give a user these privileges, open local sec policy, select Logon as service policy and add the user the user should have read access to AD to send queries

What is a Hypervisor?

There are two types of virtualization software's available from vmware. One works at application level (ex. vmware workstation & vmware server) and the other one works at Operating system level (ex.VMWare ESX server, Microsoft Hype-V, Citrix XenServer etc. These are called Hypervisors. The Hypervisor is an operating system/virtualization which directly communicate with the hardware and provides better access of resources to the virtual machines. Where as i said before, virtualization apps like vmware workstation, microsoft virtual server, vmware server will provide access of resources to virtual machines through Operating system, as those are dependent on OS and are residing at application level. So, with the help hypervisor we can take the advantage of extra-ordinary resource allocation and management. With the Hypervisor, the architecture looks like below

What is vMotion?

Moving a virtual machine from an ESX host to another while it is running. You will get a very minimum downtime for the virtual machine with this if everything configured properly. If you want to do some maintenance tasks on one ESX server in the cluster, you can vMotion all the virtual machines running on it to other ESX server which has the enough resources available. Instead of giving lot of explanation for this topic, lets see this video from VMware, i bet you will definitely become a fan of VMware with this video. :)

How to fix HA errors in VMware ESX Server?

1. Make sure all the hosts in the cluster are able to resolve each other by host name.

2. If they were not able to do so, check the DNS settings.

3. Best solution is to add all the hosts names and ip addresses into /etc/hosts file on all ESX servers in the cluster. Put the ESX server in maintenance mode before doing any changes.

4. Exit from the maintenance mode and try to reconfigure the HA on all the ESX hosts one by one, that's it your problem will be fixed.

What is VMware Consolidated Backup?

VMware Consolidate Backup is a Backup framework developed by VMware company. It is installed on Windows Server box as a proxy. Using the third party backup tools like Veritas Netbackup, Veeam Backup software's we can take backup’s of the virtual machines hosted on the ESX hosts. In detail VMware Consolidate Backup is used as mediator between the backup software and Virtual machines / ESX hosts.

It enables the backup operators to take the backup  at file level from the .vmdk files, and also enables to take snapshots. And one more important future is, its a LAN free backup solution, as the Backup Proxy server is directly connected to SAN environment (which is used by those esx hosts and virtual machines).

How it is Used?

1. As you see in the image, the backup proxy (Windows server with VM Consolidated Backup & Backup Agent) server is directly connected to the SAN.

2. The Backup agent (for ex: Veritas Netbackup / Veeam Backup) initiates the backup request through VMware Consolidated Backup, it immediately takes a snapshot of the VM  from the SAN storage and mounts the .vmdk file on the proxy server and takes the backup of the files inside the .vmdk

3. Those files are stored on to a tape drive / backup disk.

4. The main advantage of this framework is, no backup agent needs to be installed on the VM’s or ESX servers. And as it is a LAN free backup, there is no need of bringing down any of these.

Basically, here is how VCB works:

• If you are doing a file level backup, VCB does a snapshot of the VM, mounts the snapshot, and allows you to backup that mounted "drive" through VCB to your 3rd party backup software
• If you are doing an image level backup of the VM, VCB does a snapshot of the VM, copies the snapshot to the VCB server, unsnaps the VM, and allows you to backup the copied snapshot image with your 3rd party backup software.

Unable to power on the Virtual Machine, How to fix it?

If the virtual machine is running in a cluster of esx hosts, some times it won’t power on. Why because, the files that are associated with that VM are locked by the host at the time of running. So when you try to vmotion the vm from one host to another host, the first host releases those files and again locked by the second host.

So what is meant by locking here, and why it is happening?

Locking is nothing but, the registration of a vm with a host. this happens everytime when the vm is hosted on a host. this is helpful to prevent the access to the same vm for remaining hosts in the cluster.

Why the vm fails when trying to power it on?

When the files associated with that VM are locked by a host it won’t powered on. At that time, you must unregister the vm from the host using vmware-cmd utility

VMware Storage VMotion : Virtual Machine Relocation

In this article I would like to discuss about the new and outstanding technology i.e “Storage VMotion”. Till now we heard about What is VMotion? How it Happens?. With that knowledge we are going forward to learn about this new feature in vSphere. Storage VMotion is similar to VMotion in means of migrating Virtual Machine from one location to another with out downtime or without disturbance in the services. When we initiate VMotion the reference of the Virtual Machine moves from one host to another host, but not the data which is related to that VM. With Storage VMotion reference of the Virtual Machine remains in the same location, but the data moves from one location (storage) to another location (storage).

Let’s check this out how it works….

             VMware Storage VMotion allows virtual machine storage disks to be relocated to different datastore locations with no downtime, while being completely transparent to the virtual machine or the end user. 

                                                     
           

    Before moving a virtual machines disk file, Storage VMotion moves the “home directory” of the virtual machine to the new location. The home directory contains meta data about the virtual machine (configuration, swap and log files). After relocating the home directory, Storage VMotion copies the contents of the entire virtual machine storage disk file to the destination storage host, leveraging “changed block tracking” to maintain data integrity during the migration process. Next, the software queries the changed block tracking module to determine what regions of the disk were written to during the first iteration, and then performs a second iteration of copy, where those regions that were changed during the first iteration copy (there can be several more iterations).   

           Once the process is complete, the virtual machine is quickly suspended and resumed so that it can begin using the virtual machine home directory and disk file on the destination datastore location. Before VMware ESX allows the virtual machine to start running again, the final changed regions of the source disk are copied over to the destination and the source home and disks are removed. This approach guarantees complete transactional integrity and is fast enough to be unnoticeable to the end user.

               Storage VMotion facilitates us to do Storage Upgrades / Maintenance & supports to optimize the storage performance with out downtime. The best advantage of Storage VMotion is we can efficiently utilize our storage resources.

VMFS

VMware uses a file system called VMFS, which has extensive support to the clustering in VMware Environment. And also supports futures like VMotion, DRS, RDM, Snapshots etc. Here i have provided some of the Features and Limitations of Virtual Machine File Systems. This is used by all the virtual machines, and apart from this every virtual machine has its own file system like Windows VM has NTFS, Linux VM has ext2/3 FS etc. So in conclusion i can say like a file system which gives support to another file system.

Features
Allows access by multiple ESX Servers at the same time by implementing per-file locking. SCSI Reservations are only implemented when LUN meta data is updated (e.g. file name change, file size change, etc.)
Add or delete an ESX Server from a VMware VMFS volume without disrupting other ESX Server hosts.
LVM allows for adaptive block sizing and addressing for growing files allows you to increase a VMFS volume on the fly (by spanning multiple VMFS volumes)
With ESX/ESXi4 VMFS volumes also can be expanded using LUN expansion
Optimize your virtual machine I/O with adjustable volume, disk, file and block sizes.
Recover virtual machines faster and more reliably in the event of server failure with Distributed journaling.
Limitations
Can be shared with up to 32 ESX Servers.
Can support LUN's with max size of 2TB and a max VMFS size of 64 TB as of version 4 (vSphere).
"There is a VMFS-3 limitation where each tree of linked clones can only be run on 8 ESX servers. For instance, if there is a tree of disks off the same base disk with 40 leaf nodes in the tree, all 40 leaf nodes can be simultaneously run but they can only run on up to 8 ESX hosts."
VMFS-3 limits files to 262,144 (218) blocks, which translates to 256 GB for 1 MB block sizes (the default) up to 2 TB for 8 MB block sizes

FC SAN (Fiber Channel Storage Area Network) : It is the most efficient way to provide storage to the Virtual Environment. If you want to read more about SAN, please. In this technology (FC SAN), HBA cards and Optical Fiber Cables are used to Access the storage. The storage is access in the form of Blocks. And as we are using Optical Fiber cables for communication the data transfer speed is very high. VMware has limited support to the HBA cards, only some specific models are supported by VMware. The storage is allocated in the form of LUNS( A specific size of space taken from different number of hard disks) , and these LUN’s will have a unique address which is called as WWN (World wide number) and the same used to access the LUN from the ESX Server/VM. 

iSCSI SAN : It is another way of accessing the storage. In this technology the same LUN’s created and allocated for ESX server and VM’s. But the way communication is done using the Ethernet cards and RJ45 Cables. Here the identification of storage is IPaddress. It is very easy to configure and as most of the Ethernet cards are supported by VMware there is a good scope in using iSCSI SAN. And the data transfer speed is reasonable so as the Cost to implement is also very less when compared to FC SAN.

NFS ( Network File System) : This is a future of UNIX Operating Systems. You can create a NFS share in a UNIX server and the same can be made available to the ESX Server to store the virtual machines. This communication is done the same way of our regular network communication. You just need to provide the NFS share path to the ESX server in storage options, so that it will be mounted and comes available to ESX Server.

RDM (Raw Device Mappings) : Generally when we create a Virtual Machine we will create/allocate some space to the .vmdk file which is used as the internal hard disk for the Virtual Machine. We can create/allocate space for .vmdk file from the above 3 storage types. But those cannot be directly accessed by the Virtual Machine. First ESX server accesses it and it passes that access to the Virtual Machine. But using RDM we can give direct access to the Virtual Machine to the above said storages. But one disadvantage of RDM is  we cannot take snapshots if we configure it as Physical.

What is SAN? How the basic SAN environment look like ?

SAN : (Storage Area Network) A network of storage disks. In large enterprises, a SAN connects multiple servers to a centralized pool of disk storage. Compared to managing hundreds of servers, each with their own disks, SANs improve system administration. By treating all the company's storage as a single resource, disk maintenance and routine backups are easier to schedule and control. In some SANs, the disks themselves can copy data to other disks for backup without any processing overhead at the host computers.

In the above image you are able to see the basic SAN setup in larger enterprises. I will explain it now how the connectivity goes between all the devices.

What are the devices that are needed for a SAN setup?

1. SAN BOX (San Device) – It contains more number of disks to accommodate required storage to the other servers in the environment.

2. SAN NETWORK SWITCH – SAN switches are similar to normal switches but their functionality is to process storage traffic.

3.  HBA CARD : Host Bus Adapter is an interface card as NIC which resides in the normal server to initiate storage requests.

4. OPTICAL FIBER CABLES  or RJ45 CABLES : For Communication

How the communication goes now?

1. To assign more storage to the server, first it should have the HBA cards installed in it as well as the the storage devices are also comes with HBA cards by default.

2. These HBA cards are connected to SAN switch using Optical/RJ45 cables from both ends.

 3. Storage engineer creates LUN’s and allocates them to servers. Those LUN are identified by the LUN numbers. Before that, every HBA card is having its own WWN (World Wide Number) as MAC address. It is used in giving right/read access to these LUN’s. (Logical Unit Numbers) A LUN is created from an array of hard disks. It will be in any of the size.

4. Once the LUN’s are visible to the server, they can be mounted on to it in different ways because every OS has its own process to mount the LUN’s. After mounting the LUN’s they are visible as LOCAL DISKS on the server (but they ar coming from the storage area network).

5. One important point is, in FC SAN’s the data is accessible as BLOCKS with a max speed of 4MBPS, and in iSCSI SAN’s the data is accessible as files with a max speed of 1MBPS.

6. The FC SAN is very costly when compared to iSCSI SAN, because Optical Fiber Cable is used in it instead of RJ45 cable. This is the reason the transfer speed is very high. One advantage of iSCSI than FC SAN is that, it can be accessible from anywhere in the world as it relies on IP for communication as same as normal network. And its very difficult to connect the storage boxes across the world using the Fibre Cable. One it is very costly and it doesn’t rely upon IP. Even though the speed is low in iSCSI SAN, but it is the only one that is preferable in Wide Area Networks.