Friday, February 11, 2011

Virtualization FAQ



Virtualization uses software to create a Virtual Machine (VM) that emulates a physical computer. This creates a separate OS environment that is logically isolated from the host server. By providing multiple VMs at once, this approach allows several operating systems to run simultaneously on a single physical machine.
Rather than paying for many under-utilized server machines, each dedicated to a specific workload, server virtualization allows those workloads to be consolidated onto a smaller number of more fully-used machines.

Benefits

  • Consolidates multiple, under-utilized physical servers on a single host, running Virtual Machines
  • Reduces workforce/space/kilowatt by leveraging virtualization for server consolidation and agility
  • Helps save money because less managing, less space and less kilowatt hours are needed
There are some well accepted and inherit benefits to using Virtualization. Here are some of them:
  • Reduce the number of physical servers
  • Reduce the infrastructure needed for your data center (power, cooling, battery backup, network switch ports, KVM ports and space)
  • Reduce administrative overhead because servers can be administered from a single console
  • Ability to bring up new servers quickly (it could take days or weeks to put in a new physical server but it could take just a few minutes to create a new virtual server from a template)
  • Hardware Independence of virtual servers – a virtual server can run on any host server, regardless of the host hardware
  • Because of hardware independence, you receive reduce your disaster recovery cost, complexity, and recovery time
  • A “greener” datacenter & server environment due to the consolidation
  • Overall, lower TCO of servers
A hypervisor, also known as a virtual machine manager/monitor (VMM), that allows several operating systems to share a single hardware host. Each operating system appears to have the host’s processor, memory, and resources to itself. Instead, the hypervisor is controlling the host processor and resources, distributing what is needed to each operating system in turn and ensuring that the guest operating systems/virtual machines are unable to disrupt each other.

Hypervisor Classifications

Hypervisors are classified into two types:
Bare Metal/Native Hypervisors— Software systems that run directly on the host’s software as a hardware control and guest operating system monitor. A guest operating system thus runs on another level above the hypervisor. This is the classic implementation of virtual machine architectures.
Embedded/Host Hypervisors— Software applications that run within a conventional operating system environment. Considering the hypervisor layer being a distinct software layer, guest operating systems thus run at the third level above the hardware.
VMware ESX is an enterprise-level virtualization product offered by VMware, Inc. ESX is a component of VMware's. VMware states that the ESX product runs on "bare metal". In contrast to other VMware products, it does not run atop a third-party operating system, but instead includes its own kernel. Up through the current ESX version 4.0, a Linux kernel is started first, and is used to load a variety of specialized virtualization components, including VMware's 'vmkernel' component. This previously-booted Linux kernel then becomes the first running virtual machine and is called the service console. Thus, at normal run-time, the vmkernel is running on the bare computer and the Linux-based service console runs as the first virtual machine.
Hyper-Vis a hypervisor-based virtualization system for x86-64 systems.
A host system (host operating system) would be the primary & first installed operating system.  If you are using a bare metal Virtualization platform like Hyper-V or ESX, there really isn’t a host operating system besides the Hypervisor. If you are using a Type-2 Hypervisor like VMware Server or Virtual Server, the host operating system is whatever operating system those applications are installed into.
A guest system (guest operating system) is a virtual guest or virtual machine (VM) that is installed under the host operating system. The guests are the VMs that you run in your virtualization platform.
Some admins also call the host & guest the parent and child.
ESX Server and VMware Server are server virtualization products
While both ESX Server and VMware Server are server virtualization products, the difference is that VMware ESX installs and runs on the bare metal of a physical server where as VMware Server needs a base operating system. In other words, VMware ESX has a type 1 hypervisor where as VMware Server has a type 2 hypervisor.
You will obtain must better performance from ESX Server as it has much less overhead. ESX Server also has many features available such as VMFS, VMotion, VMHA, and DRS. On the other hand, ESX Server is also a commercial product that must be purchased where as VMware Server is a free product. VMware Server is an excellent option to choose to slowly migrate to server consolidation at a low cost. VMware Server is also an excellent way to learn about virtualization as well as a way to run multiple operating systems on your desktop PC, at no cost.
Like the difference between ESX Server and VMware Server, Hyper-V and Virtual server have similar differences. Hyper-V is a type-1 hypervisor where Virtual Server is a type 2 hypervisor. Virtual Server requires that you first host a Windows operating system to load it.
Hyper-V is meant to be a higher performance commercial virtualization platform with a centralized management platform and 3rd party add-ons. Virtual Server, on the other hand, is a free virtualization platform meant for the desktop or for small-scale server virtualization solutions.
emulation is where software is used to simulate hardware for a guest operating system to run in. This has been used in the past but is difficult to do and offers low performance.
Native virtualization (or full virtualization) is where a type-2 hypervisor is used to partially allow access to the hardware and partially to simulate hardware in order to allow you to load a full operating system. This is used by emulation packages like VMware Server, Workstation, Virtual PC, and Virtual Server.
Paravirtualization is where the guest operating systems run on the hypervisor, allowing for higher performance and efficiency.  For more technical information and videos on this topic, visit VMware’s Technology Preview for Transparent Virtualization. Examples of paravirtualization are Microsoft Hyper-V and VMware ESX Server.
Server Virtualization – consolidating multiple physical servers into virtual servers that run on a single physical server.
Application Virtualization – an application runs on another host from where it is installed in a variety of ways. It could be done by application streaming, desktop virtualization or VDI, or a VM package (like VMware ACE creates with a player). Microsoft Softgrid is an example of Application virtualization.
Presentation Virtualization – This is what Citrix Met frame (and the ICA protocol) as well as Microsoft Terminal Services (and RDP) are able to create. With presentation virtualization, an application actually runs on another host and all that you see on the client is the screen from where it is run.
Network Virtualization – with network virtualization, the network is “carved up” and can be used for multiple purposes such as running a protocol analyzer inside an Ethernet switch. Components of a virtual network could include NICs, switches, VLANs, network storage devices, virtual network containers, and network media.
Storage Virtualization – with storage virtualization, the disk/data storage for your data is consolidated to and managed by a virtual storage system. The servers connected to the storage system aren’t aware of where the data really is. Storage virtualization is sometimes described as “abstracting the logical storage from the physical storage.
VMware’s VMFS was created just for VMware virtualization. VMFS is a high performance cluster file system allowing multiple systems to access the file system at the same time.  VMFS is what gives you the necessary foundation to perform VMotion and VMHA. With VMFS you can dynamically increase a volume, support distributed journaling, and the addition of a virtual disk on the fly.
There are multiple ways to backup your virtual guest operating systems. As long as your critical data is sent offsite and follows your backup rotation, you are doing well.
One option would be to run a a backup client inside each guest operating system, just like you do your physical servers.
If you are using a bare metal virtualization platform (like ESX Server), the greatest challenge is sometimes gaining access to your data. For example, with ESX Server, your data is stored inside ESX Server’s VMFS file system. That file system cannot be accessed by a typical Windows or Linux backup client. For that reason, there are specialized virtualization backup products like Vizioncore’s vRanger an EsXpress.



With VMotion, VM guests are able to move from one ESX Server to another with no downtime for the users. What is required is a shared SAN storage system between the ESX Servers and a VMotion license.
Storage VMotion (or SVMotion) is similar to VMotion in the sense that it moves VM guests without any downtime. However, what SVMotion also offers is the capability to move the storage for that guest at the same time that it moves the guest. Thus, you could move a VM guest from one ESX server’s local storage to another ESX server’s local storage with no downtime for the end users of that VM guest.




15. What is VMWARE HA ?

- VMware HA (High Availability) is a utility that eliminates the need for dedicated standby hardware and software in a virtualized environment. The utility is part of a virtualization suite called VMware Infrastructure 3. In IT (information technology), the term high availability refers to a system or component that is continuously operational for long periods.
Key features of VMware HA include:
  • Proactive monitoring of all physical servers and virtual machines
  • Automatic detection of server failure
  • Rapid restart of virtual machines affected by server failure
  • Optimal placement of virtual machines after server failure
  • Scalable availability up to 32 nodes across multiple servers
When a physical server goes down or loses all network connectivity, VMHA steps in and migrates the virtual guest machines off of that server and onto another server. This way, the virtual machines can be up and running again in just the time that it takes them to reboot.


Figure 1: VMware High Availability (VMHA) - Image Courtesy of VMware.com
This is a very powerful feature because it means that any operating system and appliance can have high availability just by running inside the VMware Infrastructure.
There are a number of requirements to make this happen and there are both good and bad qualities of VMHA. I will cover all of that and show you how to configure VMHA in this article.
Let’s get started.
What is required to make VMHA work?
There are a number of requirements that you will have to meet to make VMHA work. Those requirements are:
  • VMware Infrastructure Suite Standard or Enterprise (no you cannot do it with the free ESXi nor can you do it with the VMware Foundations Suite).
  • At least 2 ESX host systems.
  • A shared SAN or NAS between the ESX Servers where the virtual machines will be stored. Keep in mind that with VMHA the virtual disks for the VMs covered by VMHA never move. What happens when a host system fails is that the ownership of those virtual machines is transferred from the failed host to the new host.
  • CPU compatibility between the hosts. The easiest way to test this is to attempt a VMotion of a VM from one server to another and see what happens. Here is what CPU incompatibility looks like when it fails:

Figure 2: CPU Incompatibility 
If you cannot achieve CPU compatibility between hosts in the HA resource pool, then you will have to configure CPU Masking (see VMworld: VMotion between Apples and Oranges).
  • Highly Recommended – to have VMware management network redundancy (at least two NICs associated with the VMware port used for VMotion and iSCSI). If you do not have this, you will see:

Figure 3: Configuration issues because there is no VMware management network redundancy
What is great about VMHA?
Here are some of the great features of VMHA:
  • Provides high availability for all virtual machines at a low cost (compared to purchasing a HA solution on a per machine basis).
  • Works for any OS that runs inside VMware ESX. That means that even if I create a Vyatta virtual router running inside ESX Server, that ESX Server is in a HA resource pool, and the server it is running on goes down, then that Vyatta virtual router OS will migrate and have it reboot on the ESX host system.
  • VMHA is easy to configure. If you have the right equipment, licenses, and VMware Infrastructure already set up, you can configure VMHA in just a few minutes.
  • Works with DRS (distributed resource scheduler) such that when a VMs are going to be brought to other hosts in the resource pool due to host failure, DRS is used to determine where that load should be placed and to balance that load.
What is “not so great” about VMHA?
Just like with any solution, there are some features of VMHA that are not as great. Those features are:
  • CPUs on each host must be compatible (almost exactly) or you will have to configure CPU masking on every virtual machine.
  • Virtual machines that are on the host system that goes doem WILL have to be restarted.
  • VMHA is unaware of the underlying applications on those VMs. That means that if the underlying application data is corrupt from an application crash and server reboot, then even though the VM migrates and reboots from a crashed machine, the application still may be unusable (not that this is necessarily VMware’s fault).
How do I configure VMHA?
Configuration of VMHA is easy, just follow these steps:
Note:
The following assumes that you already have two ESX Server host systems, the VMware Infrastructure Suite (VI Suits), the CPUs on the host systems are compatible, you have a shared storage system, and all licensing related to VMHA and the VMHA feature is in place.
  1. In the VI Client, Inventory View, Right-click on your datacenter and click on New Cluster.

Figure 4:
Adding a New HA Cluster
  1. This brings up the New Cluster Wizard. Give the Cluster a name and (assuming you are only creating a HA cluster), check the VMware HA cluster feature.

Figure 5: Naming the HA Cluster
  1. Next, you will be given a chance to configure the HA options for this cluster. There is a lot to consider here – how many hosts can fail, if guests will be powered on if the proper amount of resources is not available, host isolation, restart priority, and virtual machine monitoring. To learn more about these settings, please read the VMware 3.5 Documentation.

Figure 6: Configuring HA Options
  1. Select the swapfile location – either with the VM on your shared storage or on the host. I recommend keeping the swapfile with the VM on your shared storage.
  2. And finally, you are shown the “ready to complete” screen where you can review what you are about to do and click Finish.
  3. Once the HA cluster is created, you need to move ESX host systems into the cluster by clicking on them and dragging them into the cluster. You can also move VMs to the cluster in the same way. Here are my results:

Figure 7: HA Cluster created with ESX Server hosts and VMs inside
  1. At this point, you should click on the cluster to see if there are any configuration issues (as you see in Figure 3). Also, notice how the cluster has its own tabs for Summary, Virtual Machines, Hosts, Resource Allocation, Performance, Tasks & Events, Alarms, and Permissions.
  2. Even though I had configuration issues (no redundant management network), my VMHA cluster was still functional. To get around the “insufficient resources to satisfy configured failover level for HA” error message when powering up a VM, I changed the HA configuration to “Allow VMs to be powered on even if they violate availability constraints”.
Let’s test it.
How do I know if VMHA worked?
To test VMHA, I had two low end Dell Servers in my cluster. I had one Windows Server 2008 system running on ESX host “esx4”. To perform a simple HA test, I rebooted host “esx4” without going into maintenance mode. This caused the Windows 2008 Server to move from “esx4” to “esx3” and be rebooted. Here is the “before and after”:

Figure 8: Before causing the failure of server ESX4

Figure 9: After the failure of server ESX4 – proving the VMHA was successful
In this test, we saw that the Windows 2008 VM was moved from “esx4” to “esx3” when “esx4” we restarted.
Conclusion
In this article, you learned what VMware’s High Availability solution is and how to configure it. We started off with the requirements to use VMHA. From there, you saw what was good and what was not so good about VMHA. After showing you how to configure VMHA, I demonstrated exactly how it works in a real server failure. VMHA is really the leader when it comes to virtualization high availability.
VMware Consolidated Backup (or VCB) is a group of Windows command line utilities, installed on a Windows system, that has SAN connectivity to the ESX Server VMFS file system. With VCB, you can perform file level or image level backups and restores of the VM guests, back to the VCB server. From there, you will have to find a way to get those VCB backup files off of the VCB server and integrated into your normal backup process. Many backup vendors integrate with VCB to make that task easier. Contrary to what it sounds like VCB IS NOT a traditional backup application because it doesn’t do anything to get the data off the system and onto external media nor does it have a GUI interface.
  1. What is Virtual Center?
Both VMware Virtual Center and Microsoft System Center are centralized management applications for their respective virtualization platform.
Virtual Center is a required piece of many of the advanced VMware ESX Server features but it must be purchased separately. Virtual Center runs on a Windows server and it could use SQL as a backend.
Microsoft System Center is Microsoft’s centralized management platform for just about every Microsoft enterprise function (“from data center to desktop”, as Microsoft says).
More specifically, Microsoft System Center Virtual Machine Manager is the centralized management platform for virtualization. Microsoft calls it their “comprehensive virtualization management tool”. It can perform virtual machine monitoring, configuration, provisioning, and administration.  The latest version, VMM 2008, can manage Microsoft Hyper-V, Virtual Server 2005, and VMware ESX Server platforms.
In virtualization terminology, a partition is what is managed by a hypervisor. That partition could have a virtual guest operating system inside of it, or the partition could be empty.
From working with servers and PCs, you are familiar with common components like CPU, RAM, Disk, network, and so on.
When using server virtualization, each guest operating system will have its own virtual components such as the virtual CPU, virtual memory (RAM), virtual disk, virtual network, and so on.
Inside the guest operating system, the OS will see these devices as physical devices and you may or may not have the vendor’s virtualization driver loaded for that device. These virtual devices are configured in the virtual guest configuration for that VM, in the management interface for your virtualization software.
Type 1 virtualization platforms that run on the bare metal of your server hardware will have specific hardware requirements because they are not typical applications that run inside an underlying (host) operating system.
Because of this, type-1 virtualization platforms will have strict hardware requirements. For example, Hyper-V must run on 64 bit hardware and VMware ESX Server only support certain disk storage systems and network interface cards.
VMware Workstation snapshots allow you to preserve the state of the virtual machine so you can return to the same state repeatedly. Virtual machine snapshots can be a valuable tool to IT administrators. They provide restore points, which can minimize the damage incurred during patch or upgrade malfunction, for example. But using snapshots without understanding what they are and how they work can introduce disk space issues or malfunctioning virtual machines.
First of all, Quick and Live Migration are not the same thing. They are not synonymous or interchangeable terms. Quick Migration is completely different from Live Migration.
First of all, Quick and Live Migration are not the same thing. They are not synonymous or interchangeable terms. Quick Migration is completely different from Live Migration.
Quick Migration
Basically, it works in three steps:
1. The machine is put in “Saved” state.
2. The VM is taken by another host
3. The VM is reset.

The speed of Quick Migration does not depend on the size of the VM (size of the VHD).
Live Migration Basics
The requirements for Live Migration are similar to those for Quick Migration. The following is a rough description of the Live Migration process:
1. Pre-flight Migration. Can migration be secure and reliable?
a) Yes, migration can be and is safe.
b) If any risk or problem is detected, migration cannot occur.
2. VM Transfer.
a) Copy the VM configuration and create the worker process in the other host.
b) Move the memory pages from the current host to the new one. First move all the inactive pages you can to reduce the number of pages as much as possible.
3. Final transfer and start-up of the VM. Ideally at this point, there is a very small set of pages saved to the VM as almost all the other ones were moved to another host. The remaining few are in active state. For the final step, pause the machine, move it from one host to another, and then turn it on. Move the storage connectivity from one server to the other and it’s ready.

Many times, admins have complained that they could not access or could not boot a virtual CDROM that was inserted or an ISO file that was mapped.
And so many times, the cause of this issue is just a simply click. To access a virtual CDROM, that CDROM must be connected. If you look at the graphic below, you can see how the device is both connected and connected at power on. Connected devices are connected after the VM boots where as connected at power on devices, are connected before the VM boots. To boot a new OS CD, that CDROM needs to be connected at power on.


24. what is vmdk file ( Virtual Disk File)

The VMDK file extension is used for virtual disk files - virtual partition with data and installed operating system (Micosoft Windows, Linux, Mac OS X, MS-DOS etc.) created and used by VMware to run as a virtual machine (under host operating system).


This is a virtual disk file, which stores the contents of the virtual machine's hard disk drive.
A virtual disk is made up of one or more .vmdk files. If you have specified that the virtual disk should be split into 2GB chunks, the number of .vmdk files depends on the size of the virtual disk. As data is added to a virtual disk, the .vmdk files grow in size, to a maximum of 2GB each. (If you specify that all space should be allocated when you create the disk, these files start at the maximum size and do not grow.) Almost all of a .vmdk file's content is the virtual machine's data, with a small portion allotted to virtual machine overhead.
If the virtual machine is connected directly to a physical disk, rather than to a virtual disk, the .vmdk file stores information about the partitions the virtual machine is allowed to access.
Concerning licensing and virtualization – the most important thing to know is that any guest operating system must have a license, just as any physical server or workstation does. Thus, if you run Microsoft Virtual Server on Windows Server 2003 and 3 guest operating systems are running (Windows XP, Windows Server 2008, and Windows Vista), you must have 4 Microsoft operating system licenses – Windows XP, Windows Vista, Windows Server 2003, and Windows Server 2008.
As Linux is typically open source, you can generally have as many Linux guest operating systems as you want without paying any licensing fees. Just make sure you following the license agreement for your operating system.

Introduction

The single most popular use for virtualization, by far, is to consolidate physical servers to virtual servers. Absolutely, the easiest way to do this is to perform a physical to virtual (P2V) conversion. With a P2V conversion, you use either an imaging application or a dedicated P2V conversion application to take all data on a physical computer, move that data to the virtualized infrastructure, modify the drivers on the transferred operating system, and boot that converted virtual machine - now virtualized.
Besides performing a P2V conversion, you may also have some VMs that are virtualized on another vendor's virtualization platform. When you convert these virtual machines into your new virtualized infrastructure, this is called a virtual to virtual (V2V) conversion.

What is VMware Converter?

VMware Converter is VMware’s solution for P2V and V2V conversions. “Converter”, as they call it, comes in two different versions – Starter and Enterprise. The starter edition is free and available to everyone whereas the enterprise edition is only available to those who have Virtual Center management servers. Still, even the enterprise edition has no additional cost.
The starter edition is meant for “one off” conversions, backups, or clones of one or a few servers. With the starter edition, you can perform hot cloning, local conversions, and remote conversions to non-ESX VMware virtualization applications (Server, Workstation, or Player). A hot conversion is where you can convert a running physical machine to a virtual machine.
The enterprise edition does all that the starter edition does but it allows you to perform multiple simultaneous conversion, cold conversions using a boot CD, and it allows you to convert to ESX Server as well.
As we will be performing a hot conversion to VMware ESX Server today, I will be demonstrating VMware ESX Server Converter Enterprise in this article.
VMware describes Virtual Desktop Infrastructure (VDI) as “delivering desktops from the data center”. In other words, VDI is where enterprise desktop computers are virtualized, moved to the data center, then presented over the LAN or WAN to the end users. Once VDI is used, typically the end user devices are replaced with thin-client devices.
While VMware has a VDI product called VDM (Virtual Desktop Manager), VDI is not a product exclusive to VMware. Other VDI vendors include Citrix XenDesktop & Kidaro (now owned by Microsoft).
With VDI, virtual desktops are served by enterprise virtualization servers running products like VMware ESX, Microsoft Hyper-V, and Xen Server. With the addition of the VDI products, these desktops can be dynamically created, pooled & shared, or even accessed from a GUI menu, over a web page.
The graphic below, shows some examples of how VDI could be used and how it works.
Microsoft purchased Softgrid and has renamed it Microsoft Application Virtualization. With this software, you are able to virtualize your applications and deliver them over the network. With application virtualization, your software applications are never installed on the end user devices so there are never any software conflicts. Because of this, software testing is reduced, time to set up end user computers is reduced, and software troubleshooting is reduced. Overall, application virtualization is going to save time and money. 
Microsoft Application Virtualization competes with XenApp and VMware’s ThinApp.
In my opinion, the best free virtualization options are:
Because creating new virtualized servers is so quick and easy, many organizations have a problem with “VM Sprawl”. With VM Sprawl, the number of virtual machines (VM) running in a virtualized infrastructure increases over time, simply because of the ease of creating new VMs, not because those VMs are absolutely necessary for the business.
Concerns with VM sprawl are the overuse of the infrastructure if it is not needed and the cost of licenses for virtual machines that may not have been required.
To prevent VM sprawl, you should more carefully analyze the need for all new VMs and ensure that you are able to justify the cost of the infrastructure and the licenses for all new VMs created.
As with many server performance questions, the answer to this question is “it depends”. You can run as many VMs on a single host as your hypervisor supports (usually that is a lot) and as you have server resources for (RAM, CPU, Disk, and Network).
Typically, on a desktop PC, you can run 1-3 VMs and on a Server you can run 10-50 VMs – depending on the application demands.
VMware bought a company (Thinstall) who offered an application virtualization product. VMware renamed that product ThinApp. Similar in concept to Microsoft’s SoftGrid (now Microsoft Application Virtualization), ThinApp allows you to virtualize your applications and deliver them from servers in the data center. This prevents application conflicts, allows for easy end user device replacements, allows for easy software deployment and, overall, saves time and money.
Centralized storage (such as an iSCSI or FC SAN) is very critical to many optional virtualization features. For example, with VMware High Availability (VMHA), VMs are stored in a centralized shared data store. If an ESX Server goes down, those VMs are automatically restarted on another ESX host because that host can access them overt the centralized shared storage (SAN). Thus, while centralized storage isn’t required to use enterprise virtualization features, many of the advanced or optional virtualization features don’t work without it.
Until recently VMware’s virtualization certification was the VMware Certified Professional (VCP).  Recently, VMware announced a more advanced certification – the VCDX. To become a VCP you must complete an official VMware training course (online or in the classroom), then pass a certification test at a local training center.
The VCDX builds on the VCP. To become a VCDX, you must first be a VCP and then you are required to pass 2 more advanced tests and present a VMware Infrastructure Design plan to a certification board.
A datastore, as it is used by VMware, is a storage container for files. The datastore could be on a local server hard drive or across the network on a FC or iSCSI SAN. Inside the datastore, you will find the virtual machines, VM disks, VM configurations, and any other files you place in the datastore (such as ISO files to install a VM).
With various competing virtualization products a problem arose where different every virtualization software vendor had their own standard for packaging and distributing virtual machines. With the ability to share virtual machines over the Internet and between virtualization platforms becoming more and more important, VMware helped to create the Open Virtualization Format (OVF). The OVF is “a platform independent, efficient, extensible, and open packaging and distribution format for virtual machines”.
In my opinion, just about every server or application can be virtualized. What you need to consider is that 1) is there any specialized hardware that is required for that application which may not be supported when virtualized 2) will your virtualized servers have the resources to perform as well as the original physical server did?
Virtualized servers can support just about any amount of CPU, RAM, Disk, and Network bandwidth that is required by an application. Additionally, virtualized servers can support special peripherals such as USB, Serial (COM), and Parallel (LPT) ports for special application needs.
Of greatest concern is the virtualization of high performance applications such as SQL and Exchange. However, I have even virtualized these applications without end users noticing. Typically, the only servers that I do not virtualize are DNS servers (which are usually Windows AD Servers) as a DNS server will be needed by the virtualized servers to function.
In the end, I don’t believe that there are any drawbacks to virtualization as virtualization will save money and make server administration easier. However, just like any critical new piece of your infrastructure, server virtualization must be done right, from the beginning. You will need to spend time learning and training to learn about virtualization.
Likely, if you choose an enterprise virtualization product, you will need to spend money on virtualization software. It may also be necessary to purchase servers with more RAM (or upgrade existing unneeded servers) to be virtualization host servers (however you will be able to get rid of many servers with less RAM once they are virtualized).
If you do not already have one, you will likely need an iSCSI or Fibre Channel (FC) storage area network (SAN) to support some of the enterprise virtualization features. Also, keep in mind that as servers are more consolidated, if a single server goes down, you could loose as many as 50 virtual guest servers. With the servers being so consolidated, “all your eggs are in one basket” (or a few baskets), as they say. Because of this, you will need to choose servers that are as redundant and reliable as possible as your virtualization hosts.
Management of your virtual servers is easier than with traditional physical servers because you will have a more centralized interface for those consolidated servers. The application that you use to manage your servers will vary based on what virtualization application you use. For example, with VMware ESX Server, you will manage your servers (ie: power status, configuration, remote control) from either the VMware Virtual Infrastructure Client (VI Client) or the VMware Infrastructure Web Access interface (via a web browser). You could also manage your ESX Server via the command line using SSH.
With Microsoft Hyper-V, you would manage your server using the Hyper-V Manager MMC.


Note that this document comes without warranty of any kind. But every effort has been made to provide the information as accurate as possible. I welcome emails from any readers with comments, suggestions, and corrections at webmaster_at admin@linuxhowto.in

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