Tuesday, September 18, 2012

VMware Technical Questions and Answers and Interview FAQ -Part7- Download

61. What is the difference between a fixed and a dynamic virtual hard disk?

Some virtualization products (like MS Virtual Server and VMware Server) support two types of virtual hard drives – fixed & dynamic. What is the difference between these two types of virtual hard drives?

With both fixed and dynamic virtual hard drives, you set a maximum size that the virtual hard drive will appear to the guest virtual machine. What is different is that, with the fixed disk, the size of the disk is allocated when it is created. Thus, if you create a 100GB fixed virtual disk, 100GB in space is taken up on the host system when you create that disk.

On the other hand, when you create a dynamic virtual disk, only a tiny amount of space is taken up when you create the disk. Over time, as the amount of space used in the dynamic virtual disk is increased, the amount of real disk used on the host is increased.

While a dynamic disk is better as it uses less real space on the host disk, it is also not as preferential for performance as a dynamic virtual disk easily gets fragmented.

62. Where can I download pre-built virtual machines?

The quickest way to get started with virtualization is to download free pre-built virtual machines. These VMs already have an operating system installed and usually already have a application installed. For example, you can download Microsoft evaluation virtual machines (actually VHD files) with some of their latest enterprise applications (like Exchange Server 2007 or Windows Server 2008).

Another excellent source with hundreds of VMs available for download is the VMware Virtual Appliance Marketplace. At this site, companies and individuals have contributed VMs that anyone can download – both for commercial evaluation of software or just for fun. You will, of course, need a virtualization product. I recommend the free VMware Server or Microsoft Virtual Server & PC.

63. What are virtual machine additions and integration components?

Just about every virtualization application offers some kind of “additions” or “integration components” that you install inside your virtual machine guests. These additions are usually device drivers that increase VM performance, enable features, or make the VMs easier to manage. With VMware products, these drivers are called the “Virtual Machine Additions”. With Microsoft Hyper-V, these drivers are called “integration components”.

64. What are some of the VMware ESX Server add-ons that I should consider?

Depending on which level of the VMware Infrastructure Suite that you purchase, you may or may not get a variety of add-ons for ESX Server (such as SVMotion, VCB, VMHA, and DRS). But what other add-ons are available for VMware ESX Server and the VMware Infrastructure Suite?As ESX Server is a very mature product, there are many 3rd party products available for ESX Server.

65.Vmware Vsphere ESX 4 Best practice Configuration.

The / (or “root”) partition stores the

ESX system and all files not stored in another custom partition. If

this partition is filled to capacity, the ESX host could crash. It is

imperative to prevent this.

The swap partition is used to supplement RAM if the service console runs out

of physical memory.

The /home partition is created as a

failsafe to help prevent / from filling up. Service console accounts

(not vCenter) each have an associated /home folder. As a best practice,

administrators should not use these folders for storage. If service

console accounts are to be used and there are multiple users requiring

access, the size of this partition may need to be increased. By

default, /home is part of the / partition. By creating a custom

partition for it the / partition will be protected if /home fills to


The /tmp partition is also created as

a failsafe to help prevent filling the / partition. /tmp is often used

to untar support files, temporarily store copied logs and stage

patches. By default, /tmp is part of the / partition. By creating a

custom partition for it the / partition will be protected if /tmp fills

to capacity.

Traditionally, /vmimages was used to

store CD-ROM images (.ISOs) and Floppy Disk images (.flp, .img).

However, most organizations following best-practices have moved this

from each individual host to a single shared-storage location. However,

by default ESX creates a /vmimages folder within / . This makes it

dangerously easy for an Administrator to mistake it for the

shared-storage repository and copy images into it that will fill / . As

a failsafe to help prevent this, a small custom /vmimages partition can

be created. If the local /vmimages folder is actually used, this size

may need to be increased.

The /var partition stores most system

logs. Creating a custom /var partition provides substantial, dedicated

log storage space (/var/log) while protecting the / partition from

being filled by log files. Normally /var is part of the / partition.

260MB /boot stores the files necessary to boot the service console.

vmkcore 100MB The vmkcore partition temporarily stores log and error information should the VMkernel crash.

66.What is SWAP Partition?

To replace pages or segments of data in memory. Swapping is a useful technique that enables a computer to execute programs and manipulate data files larger than main memory. The operating system copies as much data as possible into main memory, and leaves the rest on the disk. When the operating system needs data from the disk, it exchanges a portion of data (called a page or segment ) in main memory with a portion of data on the disk.

DOS does not perform swapping, but most other operating systems, including OS/2, Windows, and UNIX, do. Swapping is often called paging or Virtual memory.

(1) Windows example

Virtual memory has been a feature of Microsoft Windows since Windows 3.1 in 1991. 386SPART.PAR (or WIN386.SWP on Windows 3.11 and Windows for Workgroups) is a hidden file created by Windows 3.x for use as a virtual memory swap file. It is generally found in the root directory, but it may appear elsewhere (typically in the WINDOWS directory). Its size depends on how much virtual memory the system has set up under Control Panel - Enhanced under "Virtual Memory." If a user moves or deletes this file, Windows will BSoD (Blue Screen of Death) the next time it is started with "The permanent swap file is corrupt" and will ask the user if they want to delete the file (It asks whether or not the file exists).

Windows 95 uses a similar file, except it is named WIN386.SWP, and the controls for it are located under Control Panel - System - Performance tab - Virtual Memory. Windows automatically sets the page file to be 1.5 x physical memory. This page file is located at C:\\pagefile.sys on all NT - based versions of Windows (including Windows 2000 and Windows XP). If you run memory intensive applications on a low physical memory system it is preferable to manually set the size to a value higher than default. Additionally, fixing the size of the swap file will prevent it from being dynamically resized by Windows. This resizing causes the swap file to become fragmented, resulting in reduced performance. This page file cannot be defragmented with Windows' built-in defragmenting tools, such as ntfsdefrag.

(2) Virtual Memory in Linux

In Linux operating system, it is possible to use a whole partition of the HDD for virtual memory. Though it is still possible to use a file for swapping, it is recommended to use a separate partition, because this excludes chances of fragmentation, which reduces the performance of swapping. A swap area is created using the command mkswap filename/device , and may be turned on and off using the commands swapon and swapoff, respectively, accompanied by the name of the swap file or the swap partition.

In order to additionally increase performance of swapping, it is advisable to put the swap partition at the beginning of the HDD, because the transfer speed there is somewhat higher than at the end of the disk. There were also some successful attempts to use the memory located on the videocard for swapping, as modern videocards often have 128 or even 256 megabytes of RAM.

67.Minimum Requirements for vCenter Server

■CPU – 2 CPUs

Processor – 2.0GHz or faster Intel or AMD processor. Processor requirements might be higher if the database ■runs on the same machine.
■Memory – 3GB RAM. Memory requirements might be higher if the database runs on the same machine.

vCenter Server includes a service called VMware VirtualCenter Management Webservices. This service requires 128MB to 1.5GB of additional memory. The VirtualCenter Management Webservices process allocates the required memory at startup.

■Disk storage – 2GB. Disk requirements might be higher if the database runs on the same machine. Microsoft SQL Server 2005 Express disk requirements – Up to 2GB free disk space to decompress the ■installation archive. Approximately 1.5GB of these files are deleted after the installation is complete. ■Networking – Gigabit connection recommended.

See your database documentation for the hardware requirements of your database. The database requirements are in addition to the vCenter Server requirements if the database and vCenter Server run on the same machine.

68.Minimum Requirements for the vSphere Client

■CPU – 1 CPU

■Processor – 266MHz or faster Intel or AMD processor (500MHz recommended). ■Memory – 200MB RAM

■Disk Storage – 1GB free disk space for a complete installation, which includes the following components: ■Microsoft .NET 2.0

■Microsoft .NET 3.0 SP1 ■Microsoft Visual J# ■vSphere Client 4.0
■vSphere Host Update Utility 4.0
You must also have 400MB free on the drive that has your %temp% directory.

If all of the prerequisites are already installed, 300MB of free space is required on the drive that has your %temp% directory, and 450MB is required for the vSphere Client 4.0.

■Networking – Gigabit connection recommended. 32-Bit or 64-Bit Operating System for vCenter Server

When you have up to 200 hosts, you can use a 32-bit Windows operating system, but a 64-bit Windows operating system is preferred. When you have 200–300 hosts, a 64-bit Windows operating system is required.

69.What is Vcenter Server?

VMware vCenter Server, formerly known as VirtualCenter, is the centralized management tool for the vSphere suite. VMware vCenter Server allows for the management of multiple ESX servers and virtual machines (VMs) from different ESX servers through a single console application.

70.Difference between HA and Vmotion?

VMotion and HA are not related and are not dependants of each other. DRS has a dependency on vMotion, but not HA. HA is used in the event that a hosts fails you can have your virtual machines restart on another host in the cluster. vMotion allows you to move a virtual machine from one host to another while it is running without service interruption. Ideally you will utilize vMotion, HA and DRS within your cluster to acheive a well balanced VI environment.

so HA fail over is not really seamless ? since you mentioned it has virtual machines restart on another host in the cluster?

no, your VM's will go down if there is a host failure and then HA will restart them on another ESX Host in the cluster. This is where DRS will take over and start to balance out the load across the remaining ESX Hosts in the cluster using vmotion.

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