ESX interview questions

1. What is Virtualization

Ans. Virtualization is an abstraction layer that decouples the physical hardware from the operating system to deliver greater IT resource utilization and flexibility. Virtualization allows multiple virtual machines, with heterogeneous operating systems to run in isolation, side-by-side on the same physical machine. Each virtual machine has its own set of virtual hardware (e.g., RAM, CPU, NIC, etc.) upon which an operating system and applications are loaded. The operating system sees a consistent, normalized set of hardware regardless of the actual physical hardware components

2. What is Hypervisor

Ans. A hypervisor, sometimes referred to as a virtualization manager, is a program that allows multiple operating systems, which can include different operating systems or multiple instances of the same operating system, to share a single hardware processor. A hypervisor must be designed for a particular processor architecture, such as the PowerPC or Intel's x86 processor. Each operating system appears to have the processor, memory, and other resources all to itself. However, the hypervisor actually controls the real processor and its resources, allocating what is needed to each operating system in turn.

Because an operating system is often used to run a particular application or set of applications in a dedicated hardware server, the use of a hypervisor can make it possible to run multiple operating systems (and their applications) in a single server, reducing overall hardware costs. Production and test systems can run at the same time in the same hardware. In addition, with a hypervisor such as the one recently discussed by Microsoft, different operating systems such as Windows and Linux can share the same server

3. How ESX do the Virtualization

Ans. It uses hypervisor to do the virtualization

4. What is Emulation

Ans. Refers to the ability of a program or device to imitate another program or device. Emulation, is quite simply the translation of software written for a different subset of hardware or for a different operating system into software which will run on the current platform. To put it quite simply its any computer program that mimics the behavior of any other piece of computer hardware, such as an older computer or video game console.

5. What is the difference between emulation and virtualization

Emulation is providing your user with a complete model of your emulated system for their use, requiring every little thing to be translated between your host and your target environments.

Virtualization is a way of exposing the "virtualized" object for shared use, in other (very loose) words, dividing the resources of your host computer into many "virtual copies" of those resources, fooling the user of each virtual copy of the host into believing that they are running on a "real" machine and have the whole machine to themselves.

Virtualization is much faster than emulation, due to the fact that you are using the "real" components rather than a software simulation.

In emulation the virtual machine simulates the complete hardware in software. This allows an operating system for one computer architecture to be run on the architecture that the emulator is written for.

6. What is Service Console

Ans. SC often called as COS (Console Operating System) is the interface

To access the ESX base operating system. ESX will interact with the

Hardware directly and SC will access the ESX in order to get the access to the hardware.

7. Is SC can be called as ESX

Ans. No Sc is merely an access point of ESX; mainly a interface of it.

8. How SC connects to the Hardware

Ans. SC mainly uses ESX to access the physical hardware layer

9. Can you VMotion the images.

Ans. No we can only VMotion the instances not the images.

10. Can you power on a template.

Ans. No. We cannot power on a template. In VI3 and VC2 we have a option to first convert the template to a Virtual Instance and then we can Power it on and do the required modifications on it and then we can again Convert it to a modified template. In ESX 2.x and VC 1.x we did not Have this capability Virtual Center 1 did not offer the ability to power on a template once Created. Now in VirtualCenter 2.,templates can be converted to virtual machines and powered on without deploying them.

11. How a VC communicate with the ESX

Ans. mgmt-vmware is service which starts and watchdogs hostd daemon.

mgmt-vmware is just a simple script that starts up hostd and vpxa. hostd

is an app that runs in the Service Console that is responsible for

managing most of the operations on the ESX machine. It knows about all the VMs that are registered on that host, the luns/vmfs volumes visible by the host, what the VMs are doing, etc. Most all commands or operations come down from VC through it. ie, powering on a VM, vmotion'ing it, creating it, etc. vpxa also runs on the Service Console and talks to VC. I believe it acts as an intermediary between VC and hostd. I think it also does some housekeeping on the ESX host, but not as much as hostd. vpxa also runs on the Service Console and talks to VC. vpxa stands for Virtual Center Agent.

vpxalogging can be modified with vpxa.cfg/etc/vmware/vpxa.cfg

Restart required for changes to take effect. service vmware-vpxa

restart is the command to restarst the vpxa.

So VC will communicate to the hostd that is in ESX via vpxa. The

service for the VC is vpxd. So vpxd will tralk to hostd via vpxa.

12. What is vpxd

Ans.

13. WHat is vpxa Service Console

Ans. vpxa also runs on the and talks to VC. I believe it acts as an intermediary between VC and hostd. I think it also does some housekeeping on the ESX host, but not as much as hostd. vpxa also runs on the Service Console and talks to VC. vpxa stands for Virtual

Center Agent. vpxalogging can be modified with vpxa.cfg/etc/vmware/vpxa.cfg Restart required for changes to take effect. service vmware-vpxa restart is the command to restarst the vpxa.

14. What is hostd

Ans. hostd is an app that runs in the Service Console that is responsible for managing most of the operations on the ESX machine. It knows about all the VMs that are registered on that host, the luns/vmfs volumes visible by the host, what the VMs are doing, etc. Most all commands or operations come down from VC through it. ie, powering on a VM, vmotion'ing it, creating it, etc.

15. What are the ports needs to be open in order to connect a ESX to a VC

Ans. There are lot of ports needs to be open but the main port which

talks to ESX from VC is TCP 902. 27000 is the port which is used for

License server.

16. What are the log files for ESX

Ans. There are plenty log files for ESX and they can be gather using a

command called vm-support. So in order to send the log files to VMware

for further troubleshooting you need to run vm-support command and it

will generate a zip file which will contain the esx log files. Those

files are:

vmkernel - /var/log/vmkernel

vmkernel warning - /var/log/vmkwarning

vmkernel summary - /var/log/vmksummary and vmksummary.txt

Host agent logs - /var/log/vmware/hostd.log

SC log - /var/log/messages

Web Access log - /var/log/vmware/webaccess

Auth log - /var/log/secure

VC Agent - /var/log/vmware/vpx

17. How do you consolidate those log files

Ans. As mentioned earlier we need to run vm-support command to

consolidate those logs

18. How do you check what are the LUNs are available to your ESX server

Ans. You can run esxcfg-mpath -l which can show this to us. vdf -h can

also show the sizes of those LUNs. fdisk -l also can show us the sizes

of the LUNs. esxcfg-vmhbadevs can show us the available LUNs to our

box.

19. How do you check the sizes available to those LUNs

Ans. vdf -h can also show the sizes of those LUNs. fdisk -l also can

show us the sizes of the LUNs.

20. Can you create a directory under VMFS2 file systems

Ans. VMFS2 is used by ESX Server v2.x and v3.x. While ESX Server 3.x

can read from VMFS2, it will not mount it for writing. VMFS2 is a flat

filesystem with no directory structure.

VMFS3 is used by ESX Server v3.x. As a most noticeable feature, it

introduced directory structure in the filesystem. Older versions of ESX

Server cannot read or write VMFS3 volumes. Beginning from ESX 3 and VMFS3,

also virtual machine configuration files are stored in the VMFS

partition by default.

21. Is vpxa required to be in middle to communicate the ESX and VC

Ans. Yes that is required. vpxa is the VC Agent which runs on esx and

act as a intermediate between hostd and vpxd.

22. What are the prerequisites for VMOTION

Ans. A dedicated Gigabit Ethernet link. A VSwitch created and dedicated

to it. The port need to be linked to the VSwitch. A portgroup needs to

be created towards this. Also a dedicated ip and a VLAN.

23. What are the prerequisites for VC2

Ans. Enough Space on this. One databse like SQL server, Oracle or

atleast MSDE.

24. What is VMNIX ?

Ans. ESX Server Service Console (vmnix). ESX Server kernel (Vmkernel).

The console is managed by vmnix kernel.

25. What is exact file where the VM data is stored

Ans. There are lot of files stored where a VM instance stored. They are

.vmdk, .nvram, -flat.vmdk, .vmsd, .vmtx, .vmxf, vmware.log. Now from

all these files the data file is the flat file. That file also can be

opened as a regular file in VI3.

25. Can you do a VMotion when processor affinity is enabled in HA.

Ans. No. When you have the processor affinity set to a VM Instance then

you cannot do a VMtion to it. As that VM is supposed to be run on

Processor X on ESX X so it does not matter whether this is a standard box

or is in Cluster.

26. What is HA and DRS?

VMware DRS (Distributed Resource Scheduling) and

VMware HA (High Availability Options).



27. How do you take the screen shot of ESX issue and a VM Windows

Instance issue?

28. What would be the best practices in order to get your ESX up and


running

29. Will you be able to see the VM after creating a Template from it

Ans. No you cannot see the VM instance after you create the template

from it. Again what you can do is you can go ahead and make a instance

from that template.

30. What is Server Consolidation

Ans. Server consolidation is an approach to the efficient usage of computer server resources in order to reduce the total number of servers or server locations that an organization requires. The practice developed in response to the problem of server sprawl, a situation in which multiple, under-utilized servers take up more space and consume more resources than can be justified by their workload.

According to Tony Iams, Senior Analyst at D.H. Brown Associates Inc. in Port Chester, NY, servers in many companies typically run at 15-20% of their capacity, which may not be a sustainable ratio in the current economic environment. Businesses are increasingly turning to server consolidation as one means of cutting unnecessary costs and maximizing return on investment (ROI) in the data center. Of 518 respondents in a

Gartner Group research study, six percent had conducted a server consolidation project, 61% were currently conducting one, and 28% were planning to do so in the immediate future.

Although consolidation can substantially increase the efficient use of server resources, it may also result in complex configurations of data, applications, and servers that can be confusing for the average user to contend with. To alleviate this problem, server virtualization may be used to mask the details of server resources from users while

optimizing resource sharing. Another approach to server consolidation is the use of blade servers to maximize the efficient use of space.

31. What are the minimum H/W requirements to install VirtualCenter Server ?

* VirtualCenter Server hardware must meet the following requirements:

Processor : 2.0GHz or higher Intel or AMD x86 processor. Processor requirements can be larger if your database server is also run on the same hardware.

Memory : 2GB RAM minimum. RAM requirements can be larger if your database is run on the same hardware .

Disk storage :Nearly 1GB free disk space

Networking : 10/100 Ethernet adapter minimum (Gigabit recommended).

Scalability : A VirtualCenter Server configured with the hardware minimums can support 20 concurrent clients, 50 ESX Server hosts, and over 1000 virtual machines.

A dual processor VirtualCenter Server with 3GB RAM can scale to 50 concurrent client connections, 100 ESX Server hosts, and over 2000 virtual machines

32. Which softwares are supported for Virtual Infrastructure Client ?

* The Virtual Infrastructure Client is designed for the 32 it versions of these operating systems:

o Windows 2000 Pro SP4

o Windows 2000 Server SP4

o Windows XP Pro (at any SP level)

o Windows 2003 (all releases except 64bit)