Over the past 18 months, the buzz around server virtualization has gradually evolved to a point where customer demand almost matches the hype from vendors. Yet the technology really is nothing new, as anyone familiar with Unix and mainframes will point out--mainframes were running virtual partitions in the 1970s. So, where exactly is all the momentum coming from?
Virtualization is a broad term, taking in the virtualisation of input/output (I/O), storage and much else, but the recent interest has been focused on virtualization of servers--essentially the ability to run more than one operating system on a single piece of hardware. While the technology for this is essentially old hat, it is relatively new to the x86 platform, with VMware--currently dominant in x86 virtualisation--getting into the game in 1998.
It's only over the past few months, however, that virtualization has really taken off on the x86 world, due to a few different factors--server replacement cycles coming around, more mature management tools for virtualized servers, support for a host of new features such as symmetric multiprocessing (SMP), where two or more processors are connected to a single memory, and growing awareness of how well virtualization works.
One result is that VMware (owned by EMC since the end of 2003) recently broke the symbolic barrier of US$100 million in revenues per quarter, a figure that has been doubling year-on-year. In February a Forrester survey of 1,221 North-American companies with more than 1,000 employees found that 41 percent were already using virtualisation or were planning pilot tests; overall, 60 percent said they would spend money on virtualisation over the next 12 months. Forty-three percent said they considered VMware most often for x86 server virtualisation, compared with 24 percent for Windows Virtual Server.
VMware is unlikely to monopolize this cash cow for long, however, with Microsoft and others keen to push their alternatives. Microsoft's Virtual Server is probably the least mature of the lot, but it is improving rapidly, and the software giant is typically giving the technology away. Moreover, virtualisation will be built into Longhorn Server within months of the operating system's release.
The other potentially disruptive development is the emergence of an open source virtualization project that seems to have nearly everyone rallying behind it. Xen, which uses a different underlying approach from Microsoft and VMware, is built into the latest Linux distributions from Red Hat, Novell and others, and is getting Solaris support within months.
A more flexible approach
Virtualization is
essentially about abstracting resources such as computing power, storage or
applications, creating flexibility in the way the resources are used. VMware was
the virtualisation pioneer in the x86 realm, and is largely responsible for its
current popularity on x86 servers, a fact even competitors readily admit.
"VMware discovered the server virtualisation market. They educated that market
for everybody," says Simon Crosby, chief technology officer of XenSource, the
commercial software company founded by Xen's creators.
In the operating system virtualization realm there are several different approaches, which can be categorised by the degree of virtualization they offer. Software such as the PowerPC version of Virtual PC, for example, emulates the hardware platform completely in software, letting you run an operating system designed for entirely different hardware. This entails a big performance hit, however. VMware and Microsoft's Virtual Server, by contrast, only virtualize enough of the hardware to allow operating systems to run in isolation, but the operating system has to be designed for the hardware it's running on. Such an approach still entails a significant processing overhead, however.
Some approaches, such as Solaris Containers, BSD jails and SWsoft's Virtuozzo, virtualise at the operating system level, reducing the load significantly. Only one type of operating system can run on a single physical machine, and all the operating system instances use the same kernel. For putting up with this limitation, the benefits are low overhead, improved performance and massive scalability--potentially hundreds of server instances per machine.
The approach taken by Xen, called paravirtualization, doesn't simulate hardware at all, instead offering an API that gives each operating system direct hardware access. This means very little overhead and the associated performance improvements, but requires modifications to the operating system. That's not a problem for an open source OS, but poses more of a problem for the likes of Windows.
The current introduction of virtualisation support in hardware--Intel's Virtualization Technology (VT) and AMD's Secure Virtual Machine (SVM)--allows Windows to run under a paravirtualizing "hypervisor" such as Xen without modification.
So what's the appeal, exactly? Back in the late 1990s, VMware's customers initially found virtualisation a useful way to build particular virtual environments for testing applications, or for testing software patches before deploying them on production systems.
Around 2001--amid budget cutbacks, and in the wake of the late-1990s server glut--users began getting seriously interested in consolidation for their production servers. (Sun estimates that most production servers are running at about 15 percent utilization). The idea was that "server sprawl" could be brought under control, and processing capacity used more efficiently, by loading a number of independent servers onto a single system. This was part of a broader trend towards "utility computing", which encompasses the idea of linking large numbers of heterogeneous servers together into a single pool of resources that virtualisation can divide up at will.
"Fundamentally, we've been approaching a crisis point in the amount of complexity, ever since the birth of client-server," says analyst Gary Barnett of Ovum. "Since the turn of the millennium, we've been reaping the results of our over-exuberance, in buying all these little bits of heterogeneous technology. People have been saying, 'Let's get this under control,' and virtualisation is one of the tools key to doing that, alongside things like clustering."
Advanced uses
According to VMware's view of
things, companies have now moved on from simple clustering services to what it
calls infrastructure virtualisation. This includes a range of advanced
management services, each of which VMware says have seen significant customer
takeup.
One is disaster recovery, in essence the capability of automatically shifting a running server from one machine to another, with little or no interruption, in the case of hardware failure. Most server virtualisation offerings now provide management software that can do this automatically, with no break in service. Virtualization also makes it much easier to back up an entire data centre; VMware says one customer, with 200 virtual machines running in a centre, can have a backup running in 20 minutes. VMware says two-thirds of its customers are using virtualisation for disaster recovery.
"Previously, if you wanted disaster recovery, the hardware, operating system and applications were all tightly linked to each other, so in your secondary data centre you had to have the same hardware, applications and the rest, and keep them all in sync," says Raghu Raghuram, VMware's vice president for data centre and desktop platform products. "With a virtual machine, you can take that file, transport it by SAN or tape or what have you, to another data centre, and get it up and running immediately".
Shifting servers from one machine to another at will makes it easier to carry out hardware maintenance and load balancing. VMware says more than half of its customers are using a tool called VMotion for such services. Other advanced applications gaining momentum among VMware users include rapid provisioning of applications and virtualisation of desktop operating systems, which some companies prefer for the greater security it provides.
Newcomers: Microsoft and Xen
VMware is keen to
point out such trends, as it believes competitors such as Microsoft and Xen are
currently nowhere near it when it comes to management tools. Microsoft is just
getting started in the field. And while Xen's hypervisor has reached a certain
level of solidity--it's now launched version 3.0 after more than three years of
development--there aren't yet Xen-based tools comparable with those found in
VMware's just-launched Virtual Infrastructure 3. "At the end of the day,
Microsoft and Xen are playing catch-up," says Gartner's Phil Dawson.
The shape of the virtualization market is changing rapidly, however, with an unmistakable trend toward universally available virtualisation built into the operating system. Microsoft's latest offering, Virtual Server 2005 R2, running on Windows Server 2003, is available for free — a price that's somewhat difficult to argue with.Virtual Machine Manager, a management tool based on Virtual Server 2005 R2, is set for availability later this year. Most importantly, Microsoft is planning to build a paravirtualizing hypervisor into Longhorn Server. "Virtualization is now commoditized," says Alfred Biehler, product manager for management and virtualization at Microsoft UK.
Xen is being built into several Linux distributions. Red Hat Enterprise Linux (RHEL) 5 will ship with Xen integrated by the end of this year. Suse Linux Enterprise 10, planned for July 2006, will also integrate Xen. Sun is planning to support Xen in OpenSolaris this autumn, and its Solaris 10 version of Unix will get Xen support in the first half of next year.
"Virtualization is going to be in the next release of every OS. It's game over," says XenSource's Crosby. "The question for VMware is, what the heck do they do about this? At the moment, we're no more than a really annoying gnat to them, but Microsoft is a truck coming full bore with its headlights on."
Gartner's Dawson agrees. "As soon as Microsoft launches their hypervisor, they're going to flood the market."
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