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Friday, October 19, 2012

Vmware Interview Questions - Part 2

Click Here for Part 1

1. Explain the physical topology of Virtual Infrastructure 3 Data Centre?

a typical VMware Infrastructure data center consists of basic physical building blocks such as x86 computing servers, storage networks and arrays, IP networks, a management server and desktop clients.

2. How do you configure Clusters, Hosts, and Resource Pools in VI3?

A cluster is a group of servers working together closely as a single server, to provide high availability, load balancing and high performance.  A host is a single x86 computing server with individual computing and memory resources. Resource pools are allocation of the available resources in to pieces for the proper distribution.

3. What are resource pools & what’s the advantage of implementing them?

A VMware ESX Resource pool is a pool of CPU and memory resources. Inside the pool, resources are allocated based on the CPU and memory shares that are defined. This pool can have associated access control and permissions. Clear management of resources to the virtual machines.

4. Explain why VMware ESX Server is preferred over Virtual Server or Workstation for enterprise implementation?

For better resource management as it has a virtualization layer involved in its kernel, which communicates with the hardware directly.

5. In what different scenarios or methods can you manage a VI3 ?

Using the Virtual Infrastructure Client we can manage one esx server, using virtual center we can manage more than 1 esx server.. and also we can use service console to manage it.,289483,sid179_gci1280576_mem1,00.html

6. Explain the difference between access through Virtual Infrastructure Client (vi client), Web access, Service Console access(ssh) ?

Using VI Client we can access the ESX server as well as Virtual Center Server also, here we can use unix type of authentication or windows type authentication. But to access the service console, we should use unix type of authentication preferably even though we can access the service console through ad authentication using esxcfg-auth, but it does not support all functions to work on, all the functions are available only with root account which is based on red hat Linux kernel. Using the web access also we can manage virtual center as well as a single host. But all the enterprise features are not supported.

Console access to the Service Console

The disadvantages to this mode are

you must be at the console (or connect using an IP KVM) and
you must know Linux to accomplish your task (no GUI).

SSH to the Service Console

You can SSH to the console prompt of an ESX server and receive the same Linux text console access as I showed above. Telnet is not allowed. To use this method, the ESX server must be working on the network and you must have an SSH client on your PC to connect. Again, in this mode, you don't get a GUI interface.

VMware Virtual Infrastructure (VI) Web Access to the ESX Server

This is the VMware VI Web Access interface. The benefit to using this is that you get a GUI client for your ESX server without having to install a client on your local machine. The downside to the web interface is that you can only perform basic ESX functions like controlling existing machines (start/stop/pause) and console remote access. You cannot add new VMs, work with VM storage, or VM networks. Still, this is a great interface if you just need to check the status of your ESX VMs, restart a VM, or use console remote control.

VMware Virtual Infrastructure Client (VI Client) to the Server

The benefits to the VI client are that you have full access to do whatever is needed on the ESX Server and you get a GUI client to do it in. The only downside is that you must install the VI client application to do this. However, the installation is negligible and the VI client is the absolute best way to administer your ESX Server.

VMware Virtual Infrastructure Client (VI Client) to the Virtual Center Server (VC Server)

From this VI VC interface, you can manage all ESX servers, VM storage, VM networks, and more. Virtual Center, of course, is an optional product that requires additional licenses and hardware.

7. Explain advantages or features of VMware Virtual Machine File System (VMFS) ?

It’s a clustered file system, excellent support for sharing between ESX servers in a cluster.


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.


Can be shared with up to 32 ESX Servers.
Can support LUNs 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.

8. What are the types of data stores supported in ESX3.5 ?

iSCSI datastores, FC SAN datastores, Local VMFS, NAS and NFS

9. How can you configure these different types of datastores on ESX3.5 ?

If we have FC cards installed on the esx servers, by going to the storage option, we can scan for the luns.

10.What is Vmware Consolidate Backup (VCB) ? Explain your work exposure in this area ?
VMware Consolidated Backup is  a backup framework, which enables 3rd party tools to take backups. VCB is used to help you backup your VMware ESX virtual servers. Essentially, VCB is a "backup proxy server". It is not backup software. If you use VCB, you still need backup software. It is commonly installed on its own dedicated Windows physical server.

Here are the benefits of VMware's VCB:

 •Centralize backups of VMware ESX Virtual Servers
 •Provide file-level backups of VMware ESX Virtual Servers - both full and incremental (file level backup available to only Windows guests)
 •Provide image-level backups
 •Prevent you from having to load a backup agent on every Virtual Machine
 •Prevent you from having to shutdown Virtual Machines to get a backup
 •Provides LAN-Free backup because the VCB server is connected to the SAN through your fibre channel adaptor
 •Provides centralized storage of Virtual Server backups on the VCB server, that is then moved to your backup tapes through the 3rd party backup agent you install
 •Reduces the load on the VMware ESX servers by not having to load a 3rd party backup agent on either the VMware ESX service console or on each virtual machine.
 •Utilizes VMware Snapshots

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.

11. How do you configure VMware Virtual Centre Management Server for HA & DRS ? What are the conditions to be satisfied for this setup?

HA & DRS are the properties of a Cluster. A Cluster can be created only when more than one host added, in that case we need to configure HA & DRS as well to provide High Availability and Load balancing between hosts and for the virtual machines.

12.Explain your work related to below terms :
VM Provisioning:  Virtual Machine  Creation.
Alarms & Event Management: Alarms are used to know the status of the resource usage for a VM. Events are used monitor the tasks that are taken place on the esx servers or in the virtual center
Task Scheduler: Task scheduler, if you want to schedule a task it will be used, for example if you want move one vm from one host to another host or if you want shutdown/reboot a vm etc.
Hardware Compatibility List: what are the hardware that compatible with ESX OS.

13.What SAN or NAS boxes have you configured VMware with ? How did you do that ?

Storage team will provide the LUN information, with that we will add those LUNs to ESX hosts from VM storage.

14.What kind of applications or setups you have on you Virtual Machines ?

Exchange server and Share Point, but these are for DEMO purposes, Cirtrix presentation servers etc.

15. Have you ever faced ESX server crashing and Virtual Centre Server crash? How do you know the cause of these crashes in these cases ?

16. Will HA work if Virtual Center Server is down ?

A1) HA continues to work if VC is down - the agents are initially configured by virtual center, but HA operations are controlled by local agents on ESX. VC does NOT monitor the ESX servers for HA. ESX servers monitor each other.
DRS do not work while VC is down.
A2) For DRS, the config and logic is completely in VC.
For HA, only the config is in VC. The logic is in the service consoles, and that's where the reaction is coming from. VC will notice the HA reaction afterwards when it connects to the service consoles the next time.
No, Why because all these futures are comes with Virtual Center only.

17. What are the situations which triggers vMotion automatically?

Resource Contention between virtual machines (DRS)
Distributed power management

18. What is DRS/HA/DPM/dvSwitch/FT/vApps/vSafe/vShields ? :-)

DRS : Distributed Resource Scheduling
HA : High Availability
DPM : Distributed Power Management
dvSwitch : Distribute vSwitch – It’s a new feature introduced in vSphere4.0
FT : Fault Tolerance for Virtual Machines – it’s a new feature introduced in vSphere4.0
vApps : vApp is a container same as resource pool, but it is having some features of virtual machines, a vApp can be powered on or powered off, and it can be cloned too.

vmSafe : VMsafe's application programming interfaces are designed to help third-party vendors create virtualization security products that better secure VMware ESX, vShield Zones is a security tool targets the VMware administrator.

vShield : VShield Zones is essentially a virtual firewall designed to protect VMs and analyze virtual network traffic. This three-part series describes vShield Zones, explains how to install it and provides useful management tips. To begin, let's get started with the basics: what vShield Zones is and how it works.,289483,sid179_gci1363051_mem1,00.html

19. What are the requirement for FT ?

20. What are the differences between ESX and ESXi ?

ESX is an OS with full features of virtualization, ESXi is a limited features OS with 32MB image.

21. Which are the new features introduced in vSphere 4 ? *****

1. 64-bit hypervisor - Although not everyone realized it, the hypervisor in ESX Server 3.5 was 32-bit. As a result, ESX Server 3.5 couldn't take full advantage of today's more powerful 64-bit hardware platforms. ESX Server 4.0 uses a native 64-bit hypervisor that provides significant performance and scalability enhancements over the previous versions. However, the new hypervisor does require a 64-bit hardware platform.

2. Increased VM scalability - ESX Server 4.0's new 64-bit architecture provides significant increases in scalability. ESX Server 4.0 supports virtual machines (VMs) with up to 255GB of RAM per VM. In addition, the vSphere 4.0 Enterprise Plus edition provides support for up to 8-way virtual SMP per VM. The other editions support up to 4-way virtual SMP. These gains are available on both Windows and Linux guests.

3. Hot add CPU, RAM, and virtual disks - This important enhancement in vSphere 4.0 is designed to create a dynamic IT infrastructure through the ability to add CPU, RAM, and virtual disks to a running VM. The hot add capability lets you dynamically increase your VMs' performance during periods of high resource demands.

4. Thin provisioning - This feature is nothing new to Microsoft virtualization users; vSphere now offers a thin-provisioning feature that's essentially the equivalent of Hyper-V's dynamic disks. Thin provisioning lets you create and provision a Virtual Hard Disk (VHD), but the host uses only the amount of storage that's actually required by the VM rather than using the VHD's allocated size.

5. VMware Fault Tolerance - Fault Tolerance is a new high-availability feature in vSphere 4.0. Fault Tolerance works only between two systems. It uses a technology called vLockstep to provide protection from system failure with absolutely no downtime. VMware's vLockstep technology keeps the RAM and the virtual processors of two VMs in sync at the instruction level.

6. vNetwork Distributed Switch—vSphere 4.0's vNetwork Distributed Switch lets you create and share network configurations between multiple servers. The vNetwork Distributed Switch spans multiple ESX Server hosts, letting you configure and manage virtual networks at the cluster level. It also lets you move network configuration and state with a VM when the VM is live migrated between ESX Server hosts.

7. IPv6 support - Another enhancement in vSphere 4.0 is support for IPv6. Many organizations are planning to move to IPv6. vSphere's IPv6 support lets customers manage vCenter Server and ESX Server hosts in mixed IPv4/IPv6 network environments.

8. vApps—vApps essentially lets you manage as a single entity multiple servers that comprise an n-tiered application. Using vApps, you can combine multiple VMs, their interdependencies, and their resource allocations together as a unit. You can manage all the components of the vApps as a single unit, letting you power off, clone, and deploy all the vApps components in the same operations.

9. vSphere Host Update Utility—The new vSphere Host Update Utility lets you centrally update your ESXi and ESX Server 3.0 and later hosts to ESX Server 4.0. The UI displays the status of the remote updates in real time.

10. VMware vShield Zones—VMware's new vShield Zones let customers enforce network access protection between VMs running in the virtual data center. The vShield Zones feature lets you isolate, bridge, and firewall traffic across vCenter deployments.

22. Which are the traffic shaping options available to configure?23. What is promiscuous mode ?

If the promiscuous mode is enabled for a switch, the traffic sent that switch will be visible to all vm’s connected to that switch. I mean, the data will be broadcasted.

24. What makes iSCSI and FC diffrent ?
Addressing Scheme, iSCSI relies on IP and FC not, and the type of transfer of data also. In FC the data transferred as blocks, in iSCSI the data transferred as files. The cabling also, FC uses Fibre cable and iSCSI uses RJ45.
25. What is the format for iSCSI addressing ?

IP Address

26. VM's Task Manager shows performance normal, But vCenter reports high resource utilization, what is the reason ?
Search KEY WORDS : VM's performance normal,  vCenter reports high resource utilization

27. What are the different types of memory management tricks available under ESX ?

28. What is vmmemctl ?

29. How we can list pNICs & status using command line ?

ifconfig –a

30. What is resource pool ? What are the use of it ?
A resource pool is a logical abstraction for flexible management of resources. Resource pools can be grouped into hierarchies and used to hierarchically partition available CPU and memory resources.

31. How HA works.
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.

32. Is HA dependent on virtual center
(Only for Install)
33. What is the Maximum Host Failure allowed in a cluster
34. How does HA know to restart a VM from a dropped Host
(storage lock will be removed from the metadata)

35.How many iSCSI targets will ESX support
8 for 3.01, (64 for 3.5)
36 How Many Fiber Channel targets
(256) (128 on Install)

37 What is Vmotion

(ability to move running vm from one host to another)

38 What is virtual SMP –
when and why should you give a vm multiple vCPUs - part of their answer whould be that best pracrtice is to start with a single vCPU because of you can run into perfomance issues do to CPU scheduling

39 Ask what version of Linux kernel does ESX run

if they are truly experienced they should say ESX is not Linux and does not use a Linux kernel - and give them an extra poijnt if they explain that the service console runs a modified version of Red Hat Ent 3 -

40 does HA use vmotion?

the answer is no - vm stops and restarts on ESX other host

41. what is the different when you use viclient connect to VC and directly to ESX server itself.

When you connect to VC you manage ESX server via vpxa (Agent on esx server). Vpxa then pass those request to hostd (management service on esx server). When you connect to ESX server directly, you connect to hostd (bypass vpxa). You can extend this to a trobleshoot case, where connect to esx see one thing and connect to VC see another. So the problem is most likely out of sync between hostd and vpxa, "service vmware-vpxa restart" should take care of it.

42. What was the most difficult VMWare related problem/issue you faced in a production environment and what were the specific steps you took to resolve it?

HA issues – because of dns problems, the hosts are unable to communicate together. Corrected by adding all servers ip’s in each server’s /etc/hosts file
VM was not powered up –because the swap file was locked by another host, when I try to power on the vm its not powering up. After releasing the lock its powered on.

43. When was the last time you called VM Support and what was the issue?

Licensing related issues.

44. What was the most performance intensive production app that you supported in VMware and what were the some of the challenges that it posed?

In exchange sharepoint demo project, getting lot of VLAN issues. (its my experience, you can say yours)

45. How would you determine that a perf intensive app is a good candidate? Spefically what tools would you use to identify candidates. Specifically inside those tools what metrics would you use?

46. What is yor philosophy on how much of the data center can be virtualized? (If the interviewer wants max virtualization, but the interviewee is not convinced that this is a good idea, this could be a deal breaker)

47. What is your opinion on the virtualization vendors (MS vs VM vs Citrix vs etc) and why? (Just trying to figure out if the candidate is keeping up with this ever changing virtualization market)

48. I beleive another good question would be to ask the candidate to briefly describe VST, VGT & EST mode and 802.1Q trunking. I say this because networking is such an important part of VMware implementations and on going support.., do you really want a VMware engineer working in your environment if they lack the knowledge of these concepts (+unless of course they are only delegated with low level permissions for generic VM operations+)

More information on these mode's can be found here:
Also ask the candidate to explain why one mode would be used as opposed to another?, remember that there can be numerous reasons for the use of different modes depending on your company/client's network, security policies etc..

49. If you are interviewing for a consultant role it would also be a good scenario to provide a brief overview of a fictional network and ask the candidate to do a whiteboard draft of how the network would be layed out if say the ESX servers have 6 NIC's or 8 NIC's etc.. etc...

50. What are notable files that represent a VM?

.vmx – configuration settings for VM
.vmxf – configuration settings used to support an XML-based VM configuration API
.vmtx – configuration settings for a Template VM (replaces the .vmx file)
.vmdk – virtual disk file. (Note: if a thick disk is used, a–flat.vmdk file that represents the actual monolithic disk file will exist but will be hidden from the vSphere Client.)
.nvram – non-volatile memory (BIOS)
.vswp – swap file used by ESX/ESXi per VM to overcommit memory, i.e. use more memory than physically available. This is created by the host automatically when powering on a VM and deleted (default behavior) when powering off a VM. Swap files can remain and take up space if a host failed prior to shutting down a VM properly. Normally the swap file is stored in the location where the VM configuration files are kept; however the location can be optionally located elsewhere—for example, locally for performance reasons and if using NAS/NFS, local swap should be used.
.vmss – suspend file (if placed into suspend power mode)
.vmsd – for snapshot management
.vmsn – snapshot file

51. Host Profiles
What licensing is required for Host Profiles? Available with vSphere Enterprise Plus edition.

52 Can Host Profiles work with ESX/ESXi 3.x hosts?
•No. Only starting with ESX/ESXi 4.0.

53 Can Host Profiles be used with a cluster running both ESX and ESXi hosts?
•Yes, but remember to use an ESX host and not an ESXi host to create a profile for use.
•In theory, Host Profiles should work with mixed host clusters, as it translates ESX to ESXi, but be careful as there are enough differences between ESX and ESXi that can lead you to make self-inflicted errors when applying Host Profiles. The easiest method is to create clusters that are homogeneous and maintain two different profiles for these two types of clusters.

54 Can Host Profiles work when using the Cisco Nexus 1000v?
•No, because Host Profiles was designed with the generic vNetwork Distributed Switch. The Cisco Nexus 1000v switch gives administrators finer-grained control of the networking beyond what Host Profiles can apply.

55. What are host profiles?
A set of best practiced configuration rules, which are can be applied to entire cluster or to an individual host. So that all the hosts in sync with each other, this will avoid vmotion, drs and ha problems.
56. Could not power on VM: no swap file
My ESXi 3.5 machine runs 8-10 VMs (Win2k3 and WinXP) normally. At the moment, 5 of them are complaining that they cannot Power On. They seem to start and then complain "Could not power on VM: no swap file". I had a look with the data browser. It's a small installation, so the vswp files ought to be in the same directory as the vmx file (I did not inttionally put them anywhere else). Of course I don't see a vswp file there because the machine is not running. I don't know enough about the vmx file structure to identify if anything is wrong in the specifications. I have downloaded one of the vmx files and attached it here. Please either tell me what to change in that vmx file, or suggest another approach to get the machines to start.
57. What are the available Storage options for virtual machines ? Raw device mappings, VMFS
There are two ways to provision storage for virtual machines (VMs) on a storage area network (SAN). One way is to use VMFS, the proprietary, high-performance clustered file system provided with VMware Infrastructure (VI). Using virtual disks (VMDK files) on VMFS is the preferred option for most enterprise applications, and as such supports the full range of functionality available in a VI implementation, including VM snapshots, VMotion, Storage VMotion, and VMware Consolidated Backup (VCB).
The other way to provision storage is Raw Device Mapping (RDM). RDMs are sometimes needed in instances where virtualized access to the underlying storage would interfere in the operation of software running within the VM. One such example is SAN management software, which typically requires direct access to the underlying hardware; and thus would need to use an RDM instead of a virtual disk. In this tip, I'll discuss what RDMs are and when to use them over a virtual disk.
Defining raw device mappings
An RDM is a file that resides within a VMFS volume that acts as a proxy, or an intermediary, for a raw physical device. One can think of an RDM as a symbolic link to a raw LUN. The RDM contains metadata and other information about the raw physical device being accessed and can, depending upon the configuration of the RDM, add features like VMotion support and snapshots to VMs that are using raw LUNs.
Why use RDMs instead of virtual disk

58. What are the differences between Virtual and Physical compatibility modes when mapping the Raw Devices to virtual machines?

You can configure RDM in two ways:
Virtual compatibility mode—this mode fully virtualizes the mapped device, which appears to the guest operating system as a virtual disk file on a VMFS volume. Virtual mode provides such benefits of VMFS as advanced file locking for data protection and use of snapshots.

Physical compatibility mode—this mode provides access to most hardware characteristics of the mapped device. VMkernel passes all SCSI commands to the device, with one exception, thereby exposing all the physical characteristics of the underlying hardware. In this mode, the mapping is done as follows, when we create a mapping, the configuration stored in a file and that file is stored with the vm files in datastore. This file points to the raw device and makes it accessible to the vm.

59. What are RDM Limitations?

RDM limitations
There are two types of RDMs: virtual compatibility mode RDMs and physical compatibility mode RDMs. Physical mode RDMs, in particular, have some fairly significant limitations:
•No VMware snapshots
•No VCB support, because VCB requires VMware snapshots
•No cloning VMs that use physical mode RDMs
•No converting VMs that use physical mode RDMs into templates
•No migrating VMs with physical mode RDMs if the migration involves copying the disk
•No VMotion with physical mode RDMs

Virtual mode RDMs address some of these issues, allowing raw LUNs to be treated very much like virtual disks and enabling functionality like VMotion, snapshotting, and cloning. Virtual mode RDMs are acceptable in most cases where RDMs are required. For example, virtual mode RDMs can be used in virtual-to-virtual cluster across physical hosts. Note that physical-to-virtual clusters across boxes, though, require physical mode RDMs.

While virtual disks will work for the large majority of applications and workloads in a VI environment, the use of RDMs--either virtual mode RDMs or physical mode RDMs--can help eliminate potential compatibility issues or allow applications to run virtualized without any loss of functionality.

1 comment:

  1. Are you making money from your exclusive shared links?
    Did you know that Mgcash will pay you an average of $500 per 1,000 unlocks?


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