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Planning your implementation of Hyper-V

Leveraging Windows 2008 server virtualization requires careful planning; because each Hyper-V guest session is a completely running operating system, you'll need to avoid bumping up against server performance limits. This excerpt from "Windows 2008 Unleashed" offers planning advice.

For the organization that chooses to leverage the capabilities of Windows 2008 virtualization, a few moments should be spent to determine the proper size, capacity, and capabilities of the host server that would be used as the virtual server host system. Many server system applications get installed with little assessment on resource requirements of the application itself, because most servers in a data center are running less than 10% server utilization, so there is plenty of excess server capacity to handle server workload capabilities.

However with Hyper-V, because each guest session is a completely running operating system, the installation of as few as three or four high-performance guest sessions could quickly bring a server to 50% or 60% of the server performance limits. So, the planning phase is an important step on a Hyper-V configuration.

Sizing Your Windows Server 2008 Server to Support Virtualization

The host Windows 2008 server needs to run Windows Server 2008 x64-bit edition. Although the minimum requirements for server compatibility for Windows 2008 applies, because server virtualization is the focus of this server system, the minimum Windows 2008 server requirements will not be sufficient to run Windows 2008 virtualization.

Additionally, although Windows 2008 theoretically has maximum processor and memory capabilities that reach into a dozen or more core processors and hundreds of gigabytes of RAM, the reality on the scaling of Windows virtualization comes down to the raw capabilities of network I/O that can be driven from a single host server. In many environments where a virtualized guest system has a relatively low system utilization and network traffic demand, a single host system could easily support a dozen, two dozen, or more guest sessions. Other environments where a virtualized guest session has an extremely high system utilization, lots of disk I/O, and significant server communications traffic I/O, the organization might find a single host server would maximize its capacity with as few as seven or eight guest sessions.

RAM for the Host Server

The rule of thumb for memory of a Windows 2008 server running Hyper-V is to have 2GB of RAM for the host server, plus enough memory for each guest session. Therefore, if a guest session needs to have 2GB of RAM and there are three such guest sessions running on the host system, the host system should be configured with at least 8GB of RAM. If a guest session requires 8GB of memory and three of those systems are running on the system, the server should be configured with 24GB of memory to support the three guest sessions, plus at least 2GB of memory for the host system itself.

Processors for the Host Server

The host server itself in Windows 2008 virtualization has very little processor I/O requirements. In the virtualized environment, the processor demands of each guest session dictate how much processing capacity is needed for the server. If a guest session requires 2 cores to support the processing requirements of the application, and 7 guest sessions are running on the system, the server should have at least 15 cores available in the system. With quad-core processors, the system would need 4 processors. With dual-core ¬processors, the system would need at least 8 processors.

With Windows 2008 virtualization, each guest session can have up to four cores dedicated to the session, or processing capacity can be distributed, either equally or as necessary to meet the performance demands of the organization. By sharing cores among several virtual machines that have low processing needs, an organization can more fully utilize their investment in hardware systems.

Disk Storage for the Host Server

A host server would typically have the base Windows 2008 operating system running on the host system itself with additional guest sessions either sharing the same disk as the host session or the guest sessions being linked to a storage area network (SAN) or some form of external storage for the virtualized guest session images.

Each guest session takes up at least 4GB of disk space. For guest sessions running databases or other storage-intensive configurations, the guest image can exceed 10GB, 20GB, or more. When planning disk storage for the virtual server system, plan to have enough disk space to support the host operating system files (typically about 2GB of actual files plus space for the Pagefile) and then disk space available to support the guest sessions.

Running Other Services on the Hyper-V System

On a system running Hyper-V, typically an organization would not run other services on the host system, such as making the virtual server also a file and print server, or making the host server a SharePoint server, or so on. Typically, a server running virtualization is already going to be a system that will maximize the memory, processor, and disk storage capabilities of the system. So rather than impacting the performance of all of the guest sessions by having a system-intensive application like SharePoint running on the host system, organizations choose to make servers running virtualization dedicated solely to the operation of virtualized guest sessions.

Of course, there are exceptions to this general recommendation. If a system will be used for demonstration purposes, frequently the host system is set up to run Active Directory Domain Services, DNS, DHCP, and other domain utility services. So, effectively, the host server is the Active Directory system. Then, the guest sessions are created to run things like Microsoft Exchange 2007, SharePoint 2007, or other applications in the guest sessions that connect back to the host for directory services.

Other organizations might choose to not make the host system the Active Directory server but rather put the global catalog functions in yet another guest session and keep the host server clean. Having a guest session host Active Directory is typically not a good recommendation, however. This is not recommended because when a host server is a member of an Active Directory domain (for the purpose of administration and management) and there is a guest session that is running as a global catalog server, if wide area network (WAN) connectivity fails so that the physical virtual server is isolated for Active Directory, the host cannot authenticate to Active Directory to even start the guest session running as a local global catalog server.

However, to get around this, if there is another server that has domain services running on it in the site, then if WAN connectivity fails, at least the virtual server host can log on to another server that is running global catalog services that is on the local network that the host resides.

Placement of global catalog services in a guest session is fine as long as the host has another external global catalog server it can depend on for authentication and that can allow domain services to start.

Planning for the Use of Snapshots on the Hyper-V System

A technology built in to Hyper-V is the concept of a snapshot. A snapshot uses the Microsoft Volume Shadow Copy Service (VSS) to make a duplicate copy of a file; however, in the case of virtualization, the file is the entire virtual server guest image. The first time a snapshot is taken, the snapshot contains a compressed copy of the contents of RAM on the system along with a bitmap of the virtual disk image of the guest session. If the original guest image is 8GB in size, the snapshot will be significantly smaller in size; however, the server storage system still needs to have additional disk space to support both the original disk image, plus the amount of disk space needed for the contents of the snapshot image.

Subsequent snapshots can be taken of the same guest session; however, the way VSS works, each additional snapshot just identifies the bits that are different from the original snapshot, thus limiting the required disk space for those additional snapshots to be just the same as needed for the incremental difference from the original snapshot to the current snapshot. This difference might be just megabytes in size.

The use of snapshots in a Windows virtualization environment is covered in more detail later in this chapter in the section titled "Using Snapshots of Guest Operating System Sessions."

Use the following table of contents to navigate to chapter excerpts

Windows Server 2008 Unleashed
  Home: Deploying and using Windows virtualization: Introduction
  1: Understanding Microsoft's virtualization strategy
  2: Planning your implementation of Hyper-V
  3:Installation of the Microsoft Hyper-V server role
  4: Becoming familiar with the Hyper-V administrative console
  5: Installing a guest operating system session
  6:Modifying guest session configuration settings
  7:Launching a Hyper-V guest session
  8:Using snapshots of guest operating systems sessions
Windows Server 2008 Unleashed covers the planning, design, prototype testing, implementation, migration, administration and support of a Windows 2008 and Active Directory environment, based on more than three and a half years of early-adopter experience in full production environments. This book addresses not only what is new in Windows 2008 compared with previous versions of the Windows Server product, but also what is different and how the similarities and differences affect an organization's migration to Windows 2008. Chapters are dedicated to the migration process from Windows 2000/2003 to Windows 2008, how to properly use Group Policies in Windows 2008, and tips and tricks on managing and administering a Windows 2008 environment. Purchase the book from InformIT.
Rand Morimoto has been in the computer industry for more than 30 years and has authored, co-authored or been a contributing writer for dozens of bestselling books on Windows 2003, Exchange 2007, security, BizTalk Server, and remote and mobile computing. Michael Noel has been involved in the computer industry for nearly two decades and has significant real-world experience with enterprise information technology environments. Michael has authored several major publications, such as SharePoint 2007 Unleashed and Exchange 2007 Unleashed Omar Droubi has been in the computer industry for more than 15 years, has co-authored one of Sams Publishing's bestselling books, Windows 2003 Unleashed, and has been a contributing writer and technical reviewer on several other books on Windows Server 2003 as well as Exchange 2000, 2003 and 2007. Ross Mistry is a seasoned veteran in Silicon Valley and has spent more than a decade in the computer industry. As a principal consultant and partner with Convergent Computing (CCO), he had the opportunity to work with Windows Server 2008 for three years before the product was released to the public. Chris Amaris is the chief technology officer and co-founder of CCO. He has more than 20 years' experience consulting for Fortune 500 companies, leading them in the selection, design, planning and implementation of complex information technology projects. Chris worked with Windows 2008 for three years before its release to the general public.

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