Introduction to Virtualization

Transcription

1 Introduction to Virtualization q q INFRASTRUC- TURES q q S CORE

2 OPTIMIZING SERVER Optimizing Server Virtualization Factoring server management and performance into consolidation projects can help optimize virtual server deployments. S CORE consolidation is easy. Making it work correctly can be a challenge. Optimizing virtual server consolidation should start with a careful look at virtualization benefits as well as tradeoffs. One immediate benefit is the use of fewer physical servers, which reduces capital hardware costs and space requirements in the data center. It can also lower collateral energy costs for power and cooling. There is often a compelling return on investment argument with these factors alone, but because there are fewer hardware devices that could fail, that saves maintenance costs as well. Fewer physical servers also mean fewer costly annual service contracts to pay. Older servers displaced in a technology refresh can be reallocated to other less critical tasks, extending the hardware s useful life. Fewer physical servers make it easier to standardize on management tools. These benefits, together with the tools used for virtual machine (VM) management, can make data centers easier to manage with fewer personnel. Consolidation can also mitigate the need to add staff as a data center grows. Perhaps the most overlooked and often understated benefit of server virtualization is enhanced flexibility. A VM is basically a file that can be moved and copied between servers and storage systems. An administrator can create and configure a new VM from a basic image in minutes. Similarly, a working VM can be migrated to a faster, more powerful server or copied to backup storage at a disaster recovery (DR) site without disrupting the machine or its users. One of the most obvious risks with server virtualization is hardware failure. In a traditional environment, a server fault would affect only the application and users running on that physical server. In a virtual environment, however, a server failure can disable all VMs that reside on it. 2 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

3 OPTIMIZING SERVER S CORE Although techniques like server clustering help maintain high availability (HA), the practices are usually reserved for mission-critical VMs and often leave secondary VMs on a single server. Consequently, administrators must track VM distribution across the enterprise to ensure that important VMs are running on adequate HA hardware. It s equally important to arrange backup cycles that meet the recovery point objective and recovery time objective for each VM. A proliferation of VMs also affects server virtualization. Just as conventional data centers faced the problem of server sprawl, the ease and speed of creating new VMs can precipitate worse conditions as administrators quickly deploy a new virtual machine for each new application or task. VM sprawl can easily lead to software licensing violations and can further complicate maintenance because there is no direct link between an application s VM and the underlying physical server. Although this abstraction is a desirable feature of virtualization, it can have undesirable consequences for careless administrators. A final issue that often goes unnoticed is VM assignment. Although a virtual machine should function on any suitable piece of hardware, it might not be prudent to combine certain VMs depending on their resource demands. Server consolidation isn t a good solution for all applications, said Rand Morimoto, president of Convergent Computing, a solution provider headquartered in Oakland, Calif. Demanding database applications can be problematic when virtualized and may cause performance problems when consolidated with other VMs on the same server, Morimoto said. ELEMENTS OF PRACTICAL SERVER CONSOLIDATION The basic premise of server consolidation is to leverage unused computing power. For example, instead of operating 10 servers at 5% utilization, operate one server hosting those 10 VMs at 50% utilization. The secret to successful server consolidation is to ensure that there are 3 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

4 OPTIMIZING SERVER S CORE adequate resources to support all VMs that will reside on the server. If the same 10 physical servers are running at an average of 15% utilization, those virtualized workloads must be spread across two or more physical servers. If they re not, then the performance of those VMs and the corresponding user experience will suffer. Prior to consolidation, each workload must be evaluated to ensure that it meets CPU, memory, I/O, storage and network connectivity or bandwidth requirements. Those factors are then combined to yield the total approximate needs for the virtualized server. There is no single recipe for sizing a physical server, and there are countless possible exceptions. When calculating memory requirements, for example, you don t need to add up all requirements for every operating system because the virtualized server will use only one OS. Similarly, you can get by with half of a CPU for every workload. As a rule, no more than two VMs per CPU should be used. A single network interface card may supply enough bandwidth for several workloads. Generally, it depends on the criticality of the applications you plan to consolidate. Server consolidation must make sense. There s no point in trying to overreduce the number of physical servers just to do it. There is nothing wrong with virtualizing a single application on a single server and forgoing consolidation, instead focusing on migration and other benefits that virtualization offers. Storage is one resource area that is frequently overlooked. Using a single huge disk drive on a virtualized machine isn t an option. Storage I/O demands from multiple VMs can seriously compromise performance. Instead, use a striped RAID array or a basic storage area network (SAN) with a separate LUN for each VM. DETERMINING AND TRACKING YOUR VM NEEDS The actual number of VMs that can be hosted on a single physical server is largely subjective. In most cases, practical resource limitations of the physical server available CPU, RAM and other computing resources will halt VM 4 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

5 OPTIMIZING SERVER S CORE growth long before any hard limits of the virtualization platform are reached. But this is also governed by the complexity and requirements of the VMs. Backup needs can greatly limit the number of virtual machines on a single server. VMs must still be protected, and traditional backups are notoriously I/O-intensive. Backing up multiple VMs simultaneously can cripple a virtual server and frequently drives other business decisions. You need to start thinking about changing the way you do things, said Pierre Dorion, data center practice director at Long View Systems, an IT solutions and services company headquartered in Denver. For example, traditional backups may be phased out in favor of VM migration tools, such as VMware Inc. s VMotion. One way to determine and track resource needs is to gather data using performance and capacity planning tools, such as IBM s Tivoli Monitoring Express and HP's Diagnostics Software, and virtualization tools such as VMware s Capacity Planner. Microsoft s Assessment and Planning Toolkit can help administrators assess their infrastructures and recommend a variety of projects. It s important to collect data over time and during peak use times. Finally, address the issue of VM assignments putting the right VMs on the right physical servers. Just because a server can be virtualized doesn t mean that it should be. Some applications, such as databases, can tax server resources and might run better if unconsolidated and kept as the only VM on a missioncritical server. Conversely, some applications that would not ordinarily coexist on the same physical server, such as SharePoint and Outlook Web Access, could easily reside on the same physical system in separate VMs. Complementary applications that would typically communicate with one another across the network may actually perform better when virtualized alongside each other on the same server. This can eliminate the slower network link and allow applications to communicate internally across the server s backplane. It s not enough to simply create new VMs and combine them based solely on available server resources. Admins must understand how VMs interoperate and use physical resources before allocating VMs throughout the enterprise. 5 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

6 MAKING VIRTUAL HIGHLY AVAILABLE Making Virtual Infrastructures Highly Available Protect production workloads by ensuring that virtual machines and the applications they run are highly available. S CORE using a high-availability strategy provides a valid approach for VM fault tolerance. But it s not always apparent which method is best for each situation. Each host runs several production VMs. If that host fails and no HA solution exists, then each VM on that failed host will also fail. This is different when you run single workloads in individual physical machines. In a case like that, there is no reason why you can t run a host-level cluster while running a guest-level HA solution such as failover clustering or network load balancing (NLB). Use these concepts in concert with your organization s existing service-level requirements to determine which level of HA you need to configure for each VM. You also must consider the support policy of the application you intend to run in the VM. WORKING WITH SINGLE-SITE AND MULTI-SITE CLUSTERS Single-site and multi-site clusters are available for host servers. Single-site clusters are based on shared storage in various forms. For example, VMware uses two key technologies for host clustering: HA and the Virtual Machine File System (VMFS), which is a sharable file system that lets multiple host servers connect to the same storage container. VMFS usually requires some form of SAN, network-attached storage (NAS) or an iscsi storage target. VMware can also perform this via the Network File System (NFS), which enables small organizations to access HA configurations for host servers. The HA VMware component then manages potential host server failures. VMware host clusters can include up to 32 nodes. Citrix XenServer can also rely on shared storage usually in the form of NFS, 6 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

7 MAKING VIRTUAL HIGHLY AVAILABLE S CORE NAS, SAN or even an iscsi target to provide HA for host servers. In a Citrix host server environment, admins can create highly available configurations by building host server resource pools. Although other hypervisors rely on management databases to control multihost configurations, each Citrix XenServer host stores its own copy of the resource pool configuration data. This removes a potential single point of failure from resource pool configurations. Citrix resource pools can also include up to 32 host nodes. Microsoft Hyper-V relies on Windows Server 2008 Failover Clustering to create host clusters. Single-site Hyper-V host clusters require shared storage in the form of SANs or iscsi targets. No other storage format is supported. Hyper-V single-site clusters can include up to 16 host nodes. It can also support multi-site clusters, which span more than one site. Because of this, the Hyper-V multi-site cluster does not require shared storage and can rely on the much faster direct-attached storage (DAS) to operate. However, to provide VM high availability, these DAS repositories must be synchronized at all times with a third-party replication tool. No matter which hypervisor you use, it s best to create host clusters when possible to provide two different levels of service continuity: 1. Host clusters support continuous VM operation. If a host fails or indicates that it is failing, all VMs running on that host will be transferred automatically to another node on the cluster. 2. Host clusters support VM operation during maintenance. If you need to work on one cluster node to install software updates, you can move VMs off of the node during operation. Move VMs back to the node once the operation is complete. Repeat this process if other cluster nodes also require maintenance. In either case, service will be interrupted while the VMs are being moved. 7 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

8 MAKING VIRTUAL HIGHLY AVAILABLE When the cluster detects that a node is failing, the cluster service causes VMs to fail over to another node. In this case, it will use a migration process to move the VM from one node to another. Depending on which hypervisor you use, this may cause a service interruption. S CORE WORKING WITH GUEST FAILOVER CLUSTERING Any VM can be made highly available when added as an application within a host cluster. But a VM is not like a traditional application. Even though the VM will always run or run as much as possible when operating on a host cluster, this model won t apply to every workload in your production network. This is because host server clustering does not affect applications contained within the VM. These applications are not aware of the host s HA feature unlike applications that are installed directly into a cluster through guest failover clustering. Host server clustering does ensure that the VM will run if a host fails. This HA model works for most applications, even though they aren t aware of it when transfers occur from one node to another. Some state-sensitive applications, such as Microsoft Exchange, do not behave properly under this model and may lose data when a transfer occurs. Transactional applications, especially those that support very high-speed transactions, do not work well with this model because they are designed to behave in a particular way when failover occurs. These applications cannot behave as planned when a VM has been failed over. Because of this, admins should consider building highly available VMs creating clusters within the VM layer to produce application-aware clusters. These clusters ensure continuous availability and stability of the applications moved into the virtual layer of a resource pool. Failover clusters work only for stateful workloads or workloads that record data from user sessions. Stateless workloads, or workloads that provide read-only services, can rely on NLB. Like failover clustering, NLB is an HA solution that s fully supported in the virtual layer. To ensure the HA of stateful applications within virtual 8 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

9 MAKING VIRTUAL HIGHLY AVAILABLE workloads, most organizations opt to run single-site clusters. These clusters are often easiest to create in the virtual infrastructure and don t require a replication engine, which often must be procured from third-party sources. S CORE WORKING WITH GUEST NLB CLUSTERS Although NLB is an HA solution, it is different than failover clustering. In a failover cluster, only one node in the cluster runs a given service. When that node fails, the service is passed onto another node, which then becomes the owner of the service. This is because of the structure of the failover cluster model. Because of this model, only one node can access a given storage volume at a time. Therefore, the clustered application can run only on a single node at one time. In NLB or server load-balancing clusters, each member of the cluster offers the same service. Users are directed to a single IP address when connecting to a particular service. The NLB service then redirects users to the first available node in the cluster. Because each member in the cluster can provide the same services, they are usually in read-only mode and considered stateless. NLB clusters are fully supported in VMs because the hypervisor network layer provides a full set of networking services, one of which is NLB redirection. This means that admins can create a multi-node cluster up to 32 NLB nodes to provide HA for the stateless services available in production VMs. However, each computer participating in an NLB cluster should include at least two network adapters one for management traffic and another for public traffic. This can be done in VMs by adding another virtual network adapter. When you run production services in VMs, make sure that the configuration is supported. Otherwise, you may need to convert the VM into a physical machine if issues arise. After that, obtain support from the vendor. Resource pool administrators should consider these configurations when preparing VMs. Supported configurations run from standalone implementations on host failover clusters to HA configurations at the guest level. When configuring VMs, always keep a product s licensing requirements in mind. 9 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

10 STORAGE IN THE VIRTUALIZED WORLD Storage in the Virtualized World Storage virtualization can improve utilization rates, keep resource costs low and boost network performance for real-world and future applications. S CORE the benefits of virtualization don t end with consolidation. Although the ability to run multiple virtual workloads on the same physical hardware is essential for server virtualization, enterprise storage can also benefit from virtualization technologies. Storage virtualization offers the advantage of aggregation allowing disparate or isolated storage resources to be pooled, provisioned and allocated regardless of their physical location within the enterprise. Storage can be virtualized in a variety of ways to achieve a balance of performance, management efficiency and flexibility. Virtualization directly affects storage efficiency. As traditional (nonvirtualized) storage needs increase and storage systems proliferate across an enterprise, unused storage resources can be orphaned through overprovisioning or simple neglect. This waste often leads organizations to invest in additional storage sooner than necessary, resulting in higher costs. Combining disparate sources reduces waste, improves utilization rates and stalls the costs of additional disk investments. For example, nonvirtualized storage use often peaks around 50%, while virtual storage utilization can frequently exceed 80%. Overprovisioning is the act of assigning more storage space to an application than is necessary. The practice is meant to prevent the provisioned volume from running out of space forcing administrators to provision new space and migrate the exhausted volume to a larger space. If the overprovisioned space goes unused, this practice can be extremely wasteful. Virtualization can also improve storage management. Without virtualization, 1 0 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

11 STORAGE IN THE VIRTUALIZED WORLD each heterogeneous storage system must be managed through a console that s unique to that particular storage system or manufacturer. Additionally, management differences may exist between products from the same vendor. Each new storage platform introduces more management overhead that administrators must deal with. S CORE STORAGE WOES Storage virtualization has a number of potential drawbacks. One issue is that the abstraction layer alone introduces complexity. Just as the hypervisor in server virtualization obscures the relationship between physical servers and the VMs that run on them, storage virtualization also obfuscates the relationship between pooled storage and underlying disks or storage subsystems. Virtual LUNs do not necessarily correlate to physical storage. This can complicate troubleshooting and problem resolution, especially as LUNs are migrated and copied between storage systems. This type of abstraction can also be a Each new storage problem when storage virtualization is platform introduces used temporarily. Most organizations more management approach storage virtualization as a permanent technology, but it s also possible overhead that administrators must deal with. for it to help with storage migration between physical systems. Using a number of diverse storage systems carries some amount of natural redundancy a failure in one storage system may not affect the availability of other applications, data or VMs. But by aggregating storage through virtualization, a problem with one storage system can affect several other virtual LUNs. In addition, organizations must be sensitive to vendor lock-in. Interoperability between storage virtualization products is often acceptable but not necessarily universal. An organization that is evaluating or selecting its storage 1 1 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

12 STORAGE IN THE VIRTUALIZED WORLD virtualization platform should consider interoperability across all of its storage systems as well as its compatibility with all its existing virtualization products. S CORE PRACTICAL STORAGE METHODS Ways to implement storage virtualization include software, appliances, switchlevel and array-level. Which method an organization chooses will depend on the barriers to entry such as cost and technical complexity, performance, flexibility, ease of use and interoperability with storage types and subsystems. Implementing storage virtualization via software, which deploys a third-party system, is often simpler and less expensive for smaller businesses. But one or more additional storage virtualization servers must be deployed to support virtualization. Software interoperability is also a common concern, partic- also be implemented Virtualization can ularly when deployed in conjunction with at the SAN switch, high-end operating systems and hypervisors. Additionally, updates or changes to possibly yielding the lowest latency and virtualization software must be thoroughly tested before rolling them out to highest performance the entire enterprise. of any approach. An appliance-based approach, such as IBM s SAN Volume Controller, features dedicated servers that already contain the hardware and software needed to implement storage virtualization. Appliances usually cost a bit more, but they offer better performance compared to software. There are also fewer risks during internal software revisions, and the appliance can typically handle heterogeneous storage. Virtualization can also be implemented at the SAN switch, possibly yielding the lowest latency and highest performance of any approach. The centralized nature of a storage switch lends itself well to centralized management. 1 2 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

13 STORAGE IN THE VIRTUALIZED WORLD Still, switch-level virtualization can be more expensive than other approaches, and the feature set may not be as rich. Storage virtualization can appear as an integrated feature of the actual storage array too. Older systems on the market virtualized only internal storage, which provided excellent performance but resisted heterogeneity and centralized management. Newer systems can include virtualization support for external storage, improving heterogeneity and making the array appear more like an appliance. S CORE WHICH METHOD IS BEST? Choosing the most appropriate storage virtualization technique can present still another challenge. Both NAS and SAN storage can be virtualized. Choosing which one to use should depend on performance and ease of use. NAS is file-based storage that s less expensive and easier for organizations to work with. SAN is block-based storage that s more expensive, but it provides better performance than NAS. Although both can be virtualized, many organizations opt to virtualize only the SAN storage, leaving NAS for secondary tasks like archival storage or backup. And although it is theoretically possible to combine NAS and SAN storage in the same pool, it s certainly not recommended because of the disparity in storage device performance. You must be cognizant to the storage access needs of each application. Furthermore, storage network architecture has little direct effect on storage virtualization choices it s merely the plumbing that ties storage to applications. Once again, cost and performance requirements should dictate choices. For example, Fibre Channel is the unquestioned leader in block-storage networking, but it s also the most expensive and sophisticated technology. On the other hand, iscsi has embraced 1 Gigabit Ethernet (GbE) and gained tremendous popularity in recent years. Ethernet-based products are much less expensive than Fibre Channel. Plus, 1 3 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

14 STORAGE IN THE VIRTUALIZED WORLD S CORE they re readily available, so management and maintenance are already understood. For many small and medium-sized companies that are considering storage virtualization, iscsi is preferable. Although Fibre Channel over Ethernet (FCoE) is still emerging, it promises another alternative that can handle high-performance Fibre Channel storage demands across standard Ethernet networks. Ultimately, all three network types should be equally suited to storage virtualization. and medium-sized For many small Although storage virtualization can pool companies that are storage and create LUNs from a potentially considering storage sizable pool, the OS that will access the virtualization, LUN ultimately limits its size. However, iscsi is preferable. huge virtual LUNs are not always the right choice. Experts are quick to point out that large LUNs can cause traffic bottlenecks. Performance problems can occur when multiple VMs are located on the same LUN. One way to maintain adequate performance is to configure and present smaller LUNs or otherwise limit the number of VMs placed on a single LUN. Large LUNs can also pose problems when restoring data to VMs. During a rollback, all of the VMs on that LUN would need to be rolled back, potentially causing unexpected data loss. It also takes longer to restore the LUN on another machine in order to recover necessary pieces of lost or missing data. Smaller LUNs avoid this type of potential contention. Administrators must be concerned with overall reliability and vulnerabilities found in single points of failure in any virtual storage infrastructure. Some high-availability storage may guard against trouble by implementing redundant storage arrays, but the added layer of protection may inflate costs and reduce application storage performance. Look for quality-of-service features that allow storage performance to be optimized for certain applications or data types. 1 4 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

15 HYPERVISORS: AT S CORE Hypervisors: At Virtualization s Core No data center administrator should implement a virtual environment without knowledge of hypervisor selection, deployment and management. S CORE virtualization technology that relies on a hypervisor software that resides between the hardware and the operating system opens the door to new levels of hardware consolidation and workload flexibility. But to take advantage of the benefits of virtualization, IT professionals must possess basic hypervisor knowledge and understand its implications. Simply stated, a hypervisor creates a layer of abstraction that isolates an OS and its associated applications from the underlying computing hardware. This effectively mitigates software from its traditional reliance on hardware devices and their drivers. The implications of this behavior are profound. A hypervisor allows operating systems and their application workloads to run on a broader array of hardware. Similarly, multiple OSes and workloads each a unique virtual machine or VM instance can reside on the same system to simultaneously share computing resources. Each VM can be migrated between computing platforms on demand with little if any processing disruption. The result is better use of computing platforms with seamless workload migration and backup capabilities. BARE METAL VS. HOSTED HYPERVISORS Hypervisors generally fall into two categories: bare metal and hosted. A baremetal (Type I) hypervisor, which is the most common type, installs directly onto the computing hardware. The OS installs and runs above the hypervisor. Major virtualization products can be called bare-metal hypervisors, including Oracle VM, VMware ESX Server, Microsoft Hyper-V and Citrix XenServer. Some bare-metal hypervisors can also be embedded into the firmware suite 1 5 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

16 HYPERVISORS: AT S CORE S CORE of the computing platform the same level as the motherboard BIOS. Examples of this approach include Hitachi Virtage, VMware ESXi and Linux KVM, a kernel-based VM. Alternately, a hosted (Type II) hypervisor is an application that runs Hypervisors don t within the OS, allowing additional OS simply manage virtual and application instances to run on instances. Current top. VMware Server and Microsoft hypervisors actively Virtual Server as well as numerous endpoint-based virtualization platforms like VMware Workstation, Mi- platform for better manage the computing crosoft Virtual PC and Parallels control and resource Workstation are hosted hypervisors. allocation to the instances that depend on their Hypervisors don t simply manage unique processing needs. virtual instances. Current hypervisors actively manage the computing platform for better control and resource allocation to the instances that depend on their unique processing needs. There s intelligence in the underlying hypervisor for performance balancing so that I can run applications inside virtual machines, said Chris Wolf, senior analyst at the Burton Group, an IT research and advisory firm headquartered in Midvale, Utah. SCRUTINIZING HYPERVISOR FEATURES The ability to support and nondisruptively move multiple workloads is fundamental to hypervisors, but there are other features that should be evaluated for an enterprise virtualization platform: D Workload support. Ensure that a hypervisor is fully tested and compatible with the OSes that you intend to virtualize. For example, Citrix XenServer can 1 6 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

17 HYPERVISORS: AT S CORE S CORE support VMs on Windows Server 2000 through 2008, Windows Vista, Windows XP SP3 and a variety of Linux distributions. Other systems may not operate properly as virtual machines. Also, think about the applications that make up a workload. Many current enterprise applications can support virtualization, but some may not perform well in a VM. Although it isn t as much an issue with processor-intensive programs, it can happen with some I/O-intensive applications. To evaluate the hypervisor s scalability and its ability to handle additional workloads as well as oversubscribed physical CPU cores, run multiple workloads on the same processor. Some workloads behave best with a traditional 1:1 ratio of physical cores to VMs. Other workloads, such as test and development or virtual desktops, may demand access to additional cores. D Processor acceleration requirements. Intel VT and AMD-V processors include hardware assistance for virtualization. Although both approaches differ, each affects the way that memory is handled in an x86 architecture. Hypervisors like Microsoft Hyper-V may require Intel VT or AMD-V processors, so it s important to know that your servers meet system requirements for the intended hypervisor. D Power management and resource optimization support. This is an increasingly important issue for energy-efficient data centers. Hypervisors generally don t support traditional sleep states like standby or hibernate. These features won t work when the hypervisor is enabled. The hypervisor should provide some support for power management and afford a level of control over processor power consumption as server utilization changes. If the hypervisor doesn t handle power management directly, it should interface with power management capabilities in the OS or other performance management software. The hypervisor should also be able to move system resources around allocating more or less computing power depending on the unique resource needs 1 7 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

18 HYPERVISORS: AT S CORE of each workload. One example of this capability is VMware s Distributed Resource Scheduling utility. S CORE D System device support. Some virtual devices are not available to a VM usually because of missing or inadequate driver support. The hypervisor may not support older network adapters or SCSI controllers under certain OSes. Similarly, USB device support is often absent under VMs in a production environment. Verify hypervisor support if your server uses legacy adapters or controllers as well as USB devices. D Security. The challenge with hypervisors is that a security breach in one workload, or in the hypervisor level itself, can potentially jeopardize all other workloads on a server. This makes security a high priority for administrators who should protect applications such as directory services integration, administrative action logs and role-based access controls. D Resiliency. Virtualization can improve the reliability of a server and its network by adding HA, fault tolerance, business continuance and DR features. In some cases, resiliency may be a matter of migration moving a workload from a failing server to a working server or spinning up a failed instance from storage onto an auxiliary server. In other cases, multiple instances of the same workloads can run redundantly across multiple physical servers, reducing recovery time when a fault occurs. D Robustness. There are few features or capabilities that are noticeably absent from modern hypervisors most of them are already quite capable. But virtualization experts point out several hypervisor capabilities that can certainly be added or improved. Having the ability to overcommit memory to allocate more memory than what s available would be noteworthy for memory-intensive virtualization tasks, especially desktop virtualization, where many instances can quickly sap 1 8 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

19 HYPERVISORS: AT S CORE memory space. Security features are another facet of hypervisors that could benefit from some improvement, but the primary need would be better integration with VM management tools. S CORE SUCCESSFUL HYPERVISOR DEPLOYMENT When planning a hypervisor deployment, don't just think about the current environment. From a practical perspective, the move to virtualization involves some amount of vendor lock-in. When you commit to a hypervisor, you re probably committing for at least three to five years, Wolf said. Make sure the technology aligns with the longterm strategic vision of your company. Hypervisor deployment is relatively simple. It s installed as software in a way that s similar to that of an OS or critical application. Embedded hypervisors don t require any installation per se because the firmware is already provided in the system hardware itself. Success with any newly installed hypervisor will depend on several factors. First, all hypervisor deployments will impose a performance penalty on the workload. It s a small penalty, and hypervisor efficiency is constantly improving, but administrators must test applications, especially I/O-intensive workloads. Workload planning and balancing can offset small penalties. New hardware platforms can be deployed to support the most demanding tasks. Workload balance is also reflected in consolidation, and experts underscore the importance of balancing consolidation levels with recovery needs. If a 4U server fails with 60 VMs on it, then I have 60 applications that are offline that IT has to deal with, Wolf said. Even if I have high availability implemented, that s still 60 applications offline for a couple of minutes until those VMs can be restarted. 1 9 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

20 ABOUT THE AUTHORS S CORE Stephen J. Bigelow, a senior technology writer in the Data Center and Virtualization Media Group at Tech- Target Inc., has more than 15 years of technical writing experience in the PC/technology industry. He holds a bachelor of science in electrical engineering, along with CompTIA A+, Network+, Security+ and Server+ certifications, and has written hundreds of articles and more than 15 feature books on computer troubleshooting, including Bigelow s PC Hardware Desk Reference and Bigelow s PC Hardware Annoyances. Contact him at sbigelow@techtarget.com. Danielle Ruest and Nelson Ruest are IT experts focused on virtualization, continuous service availability and infrastructure optimization. They are authors of multiple books, including Virtualization: A Beginner s Guide for McGraw-Hill Osborne, as well as the MCTS Self-Paced Training Kit (Exam ): Configuring Windows Server Virtualization from Microsoft Press. Download a free copy of Chapter 8: Securing Hosts and Virtual Machines for more information on Hyper-V security. Cathleen Gagne Editorial Director cgagne@techtarget.com Jo Maitland Senior Executive Editor jmaitland@techtarget.com Colin Steele Senior Site Editor csteele@techtarget.com Christine Casatelli Managing Editor ccasatelli@techtarget.com Jeannette Beltran Associate Managing Editor jbeltran@techtarget.com Linda Koury Director of Online Design lkoury@techtarget.com Marc Laplante Publisher mlaplante@techtarget.com 2011 TECHTARGET. ALL RIGHTS RESERVED. 2 0 I N T R O D U C T I O N T O V I R T UA L I Z A T I O N

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