High Availability from the Windows Server Family Side
To enhance system uptimes, there have also been numerous system architecture enhancements in Windows 2000 and 2003, such as improved memory management and driver verification, that directly reduce unplanned downtime. New file protection capabilities prevent new software installations from replacing essential system files and causing failures. Additionally, Windows device drivers and operating system files have been digitally signed by Microsoft to ensure their quality. A Microsoft digital signature is your assurance that a particular file has met a certain level of testing, and that the file has not been altered or overwritten by another program's version of the same device driver. Looking forward to Windows 2005 and as x86 server platforms have continued to make dramatic improvements in price-to-performance value, software technologies have evolved to help businesses more effectively harness that improved performance in a manageable way. Virtual machine technology (Virtual Server 2005) is one such technology.
Microsoft Virtual Server 2005
Virtual Server 2005 is the cost-effective virtual machine solution designed on top of Windows Server 2003 to increase operational efficiency in software testing and development, application migration, and server consolidation scenarios. Virtual Server 2005 is designed to increase hardware efficiency, help boost administrator productivity, and is a key Microsoft deliverable toward their Dynamic Systems Initiative (eliminating reboots of servers—that directly affects downtime!). As you can see in Figure 12.6, the host operating system—Windows Server 2003—manages the host system itself (at the bottom of the stack).
Virtual Server 2005 provides a Virtual Machine Monitor (VMM) virtualization layer that manages virtual machines, providing the software infrastructure for hardware emulation. As you move up the stack, each virtual machine consists of a set of virtualized devices, the virtual hardware for each virtual machine.
A guest operating system and applications run in the virtual machine—unaware, for example, that the network adapter they interact with through Virtual Server is only a software simulation of a physical Ethernet device. When a guest operating system is running, the special-purpose VMM kernel takes mediated control over the CPU and hardware during virtual machine operations, creating an isolated environment in which the guest operating system and applications run close to the hardware at the highest possible performance.
Virtual Server 2005 is a multithreaded application that runs as a system service, with each virtual machine running in its own thread of execution; I/O occurs in child threads. Virtual Server derives two core functions from the host operating system: The underlying host operating system kernel schedules CPU resources, and the device drivers of the host operating system provide access to system devices. The Virtual Server VMM provides the software infrastructure to create virtual machines, manage instances, and interact with guest operating systems. An example of leverage Virtual Server 2005 capabilities would be to use it in conjunction with your Disaster Recovery needs.
Virtual Server 2005 and Disaster Recovery
Virtual Server 2005 enables another form of server consolidation through disaster recovery. Rather than maintaining redundancy with costly, physical servers, customers can use Virtual Server 2005 to back up their mission-critical functionality in a cost-effective way by means of virtual machines. The Virtual Machine Monitor (VMM) and Virtual Hard Disk (VHD) technologies in Virtual Server 2005, coupled with its comprehensive COM API, can be used to create similar fail-over functionality as standard, hardware-driven disaster recovery solutions. Then, customers can use the Virtual Server COM API to script periodic duplication of physical hard disks containing vital business applications to virtual machine VHDs. Additional scripts can switch to the virtual machine backup in the case of catastrophic failure. In this way, a failing device can be taken offline to troubleshoot, or the application or database can be moved to another physical or virtual machine. Moreover, because VHDs are a core Virtual Server technology, they can be used as a disaster recovery agent, wherein business functionality and data can be easily archived, duplicated, or moved to other physical machines.