To help you decide which solution best suits your company's needs, Tech Update interviewed these three vendors. VMware CEO Diane Greene, SWsoft CEO Serguei Beloussov, and Michael Shaler, Connectix director of product management, described their companies' approaches to server virtualisation, product positioning, and their visions of the future of virtual servers.
Approaches to server virtualisation
We asked each vendor to explain why their approach to server virtualisation is unique.
Vmware's Diane Greene said, "Our virtual machine software virtualises the Intel platform so you can run multiple operating systems and applications at the same time. We do this by providing hardware-level virtualisation through the use of virtual machine technology. A VMware "partition"--or virtual machine (VM)--presents a complete set of virtual Intel x86-compatible hardware to the operating system image running within the VM. This virtual hardware provides a virtual implementation of every device found on a real server--from the motherboard chipset to the CPU and memory to SCSI and IDE disk devices to ports and display devices. [And] each virtual machine is encapsulated in a file, providing the ability to move workloads from system to system seamlessly."
Greene added, "We run close to the physical hardware in two distinct ways. First, across all our products, our VMs execute most CPU instructions directly on the system processor without intervention from our virtualisation layer. Second, in the case of ESX Server, we actually run the virtualisation layer directly on the hardware itself, without requiring a host operating system at all. When we do this, we can "take over" the hardware and precisely control the physical resources consumed by each virtual machine down to specific levels of network bandwidth or even disk I/O access. Virtual machine technology running on top of a host OS cannot achieve this level of control."
Greene added that VMware technology provides partition isolation. "To have true performance isolation, every partition should be able to count on having access to a certain amount of system resources, including disk I/O and network bandwidth. For security isolation, a malicious user in one partition should not be able to hack through to another partition."
Michael Shaler described Connectix's Virtual Server approach as "offering" two core technological competencies: virtualisation, which means to implement in software what previously existed in hardware, and binary translation, which means that we translate one instruction set to another (x86 to PowerPC, or x86 to virtualised x86 instructions) ... We support a broad range of guest OSs--we can run OS/2 and NetWare with complete driver compliance on those platforms." Virtual Server can also run Linux, Windows NT, 2000, and .Net servers.
Virtual Server echoes VMware's GSX Server in that it runs guest OSs on an existing host OS, and offers a similar approach to portability. Shaler explained, "Our 'virtual hard drives' (VHDs) feature a level of portability--[which means] the ability to access and move a complete self-contained server environment wherever needed on the network--that delivers instant-on deployment and instant undo. A virtual hard drive is similar to an OS image file, but differs in that you can boot from a read-only VHD that resides on the file system and save all disk writes to a 'differencing' drive that can either be merged with the boot drive or be discarded [i.e., instant undo]."
Shaler continued, "What we mean by 'instant-on' deployment is that a VHD residing on the file system can be accessed and booted remotely for capacity-on-demand deployment of additional server resources."
Serguei Beloussov said SWsoft's Virtuozzo takes a somewhat different approach. "[Virtuozzo] virtualises the operating system (OS) layer on Intel-based servers, creating fully-isolated virtual partitions, implementing functional, fault, namespace, and resource isolation between partitions. [This approach] produces less than 1 percent total overhead per server regardless of the number of virtual environments/partitions on that server. Our technology modifies the base kernel (right above the root OS) and creates fully-isolated virtual environments (VEs) that are instances of that same OS. Each VE can scale to 64GB RAM across 16 CPUs, and each partition can fairly and dynamically share server resources. A single kernel at the base of the server is aware of all of the applications, sites, etc., housed with each of the virtual partitions, and monitors and tracks changes in each. What's more, you can drag and drop VEs between physical servers, all from the management console."
Speaking of management, Beloussov explained, "Each of VEs is fully isolated and can be managed from a management console that enables the user to monitor VEs, applications, bandwidth, memory, I/O, and other resources levels."
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