Virtualization is actively being used by Sybase IT to help solve power/cooling issues as well as transform the datacenter into an environment that brings greater benefits to their customers, especially the engineering organization. Average CPU utilization was very low on physical servers and through virtualization this has improved considerably.

Through virtualization, IT has provided a more agile and cost-effective environment and is helping internal customers meet their objectives in a more timely manner. Many Sybase products have been proven to run in virtualized environments and the use of virtual appliances has greatly helped in the rapid deployment of new IT applications based on Sybase products. Virtual appliances are also beginning to be used as a software distribution mechanism to external customers. This article will cover the use of virtualization within Sybase and explore some use cases focused on Sybase products running on a virtualized infrastructure. Sybase customers should find this especially useful as it will show how they can rapidly create test/dev environments of Sybase products with virtualization even when it involves something as complex as the new ASE Cluster Edition.

What Is Virtualization?
Even though there is a lot of buzz around virtualization, it can still be a subject of confusion. We will begin by giving a brief overview of server virtualization. In the physical server world there is typically a one-to-one mapping of machine and operating system instance. The operating system requires at a minimum, a processor, memory, hard disk and input/output (also known as I/O) devices. The operating system is loaded on the physical server, an identity is given (name and IP address), and you are ready to run applications and establish network communications. Figure 1 shows a typical server with an operating system instance. The operating system interacts directly with the physical devices and has exclusive access to them.

With virtualization a layer is inserted between the hardware and the operating system. This layer presents the components of the hardware as logical devices to the operating system. With this layer, when the operating system is installed, it believes that the logical devices (CPU, memory, disk, etc.) are the real hardware and works just as it would if running directly on the hardware. As the devices are logical, multiple instances can be created and this allows additional copies of the operating system to be installed on the same hardware even though each instance believes it has exclusive access to the hardware. The virtualization layer is called a hypervisor and is a sort of specialized operating system that installs directly on the hardware and its purpose is only to allow interaction of guest operating systems with the hardware (see Figure 2). It handles the sharing of the hardware resources among the various OS instances.

There are variations of virtualization and not all forms rely on a hypervisor. One form is known as paravirtualization. This approach is where the guest OS is aware that it is in a virtualized environment and interacts directly with the host OS's device drivers. This makes the virtualization software cheaper because the vendor does not have to devote much energy to writing device drivers at the hypervisor level. In addition performance is improved as not all I/O has to go through the hypervisor. On the other hand the guest OS also needs some modifications to make it work with paravirtualization and this creates its own challenges.