Buyers' Guide
Xeon Buyer’s Guide: Virtualisation
Published: 13 Oct 2008, 01:01am
Virtualisation is sweeping through server rooms - and for good reason. It leads to increased control, greater flexibility and reliability and huge savings.
Virtualisation is simple, but very powerful. Instead of running directly on the physical server, each application gets a "virtual machine", a copy of the physical server provided by virtualisation software known as a hypervisor.
The hardware is abstracted away and one server can support any number of virtual machines. Multiple operating systems and different applications sit alongside each other, each effectively with its own server.
What's so good about that? It lets IT departments get better utilisation of their physical assets. When organisations install multiple servers for different applications, each has its own memory, storage and demands for power. All of which have to be provided with plenty of spare capacity. That results in massive inefficiency.
"There are more than 30 million servers in the world, and most are running at below 10 per cent utilisation," says Intel solutions architect William Crowe.
There have been efforts to consolidate those servers for a many years, but virtualisation is the first technology to really get to grips with the problem.
"Virtualisation lets you run as many as 10 to 20 applications on a single physical host, increasing utilisation to more than 50 per cent," says Crowe.
Typically most IT managers will aim to cap the utilisation at around 60 per cent maximum to ensure there is enough headroom, or elasticity, to allow applications to expand depending on variation or spikes in workload.
One server can do the job of seven or eight, saving vast amounts of resources. Intel has an online tool to help estimate the cost savings that can be made by virtualising and consolidating servers.
The technology is also taking off rapidly. In 2007, 35 per cent of new servers were virtualised. In 2008 that figure will be 52 per cent, according to research by analyst IDC.
Virtualisation technology companies VMware and Citrix are ready to push the technology even further, in "cloud computing" versions where service providers offer virtual machines to several customers.
"Virtualisation is the most important technology that will bring together sets of inherently sequential software, with defined limits to its scalability, onto a single platform that operates at high levels of utilisation," says David Mitchell, senior VP for IT research at global advisory and consulting firm Ovum.
But how can a fundamental change in the technology landscape like this move so fast? The secret is in the hardware. It has evolved to make virtualisation fly.
Early virtualisation technology had to work hard. It needed to hide the details of the hardware from the operating system, but couldn't do it perfectly. The hypervisor had to translate software calls where necessary and the operating systems had to be specially compiled in virtualisation-friendly "guest" versions.
"As virtualisation becomes a mainstream technology, we need server platforms that are designed for virtualisation," says Crowe.
Intel Virtualisation Technology provides that new architecture upon which the operating system can run directly, and removes the need for binary translation. This does away with the performance overhead that virtualisation used to suffer, and allows for simpler software, so hypervisors can be written to common standards and operate robustly.
Server design
Virtualisation doesn't stop at the processor. Within the server the memory subsystem and network interface must also be optimised, so different applications can share them without creating bottlenecks in the system that can impact system performance.
From a server architecture perspective, there are two key areas for consideration:
- Overall raw server performance: This has a major bearing on how many virtual machines you can run on a given server, also known as VM density to consolidation ration. In simplistic terms, the more raw grunt you have, the more VMs you can host at a given utilisation point.
- Hardware-based optimisation: These features improve the server’s ability to operate in a virtualised environment. These optimisations are typically targeted towards the CPU, the memory and the I/O subsystems. The goal is to remove the performance penalty introduced from having a Hypervisor carrying out the necessary translations. You are trying to get to get to a theoretical point where an application could run as well in a virtualised environment as it would in a native environment.
When you have 10 applications on a server, they may have to share the server's single NIC card," says Crowe.
Today the Hypervisor assumes the role of having to queue Ethernet traffic and map this to the individual virtual machines. This is a significant load on the CPU and Intel’s Virtual Machine Device Queuing (VMDQ) technology offloads this queuing to the physical NIC card, freeing up the CPU cycles.
This also has an effect of dramatically increasing the efficiency for getting Ethernet traffic in and out of the server and can actually double the effective throughput to around 9GB/sec.
Moving applications
Beyond the single server consolidation usage model virtualisation now allows virtual machines to move between servers in a pool, or even across wide area links. Functions like VMware's VMotion deliver this, but the job is made more efficient using new processor features such as Intel VT FlexMigration, included in the new Intel Xeon5400 and 7400 processor series.
"In future we can see more advanced usage models for virtualisation that enable the rapid provisioning of applications, and the ability to dynamically move applications across physical machines, or even between physical, geographically dispersed, data centres," says Crowe.
Moving applications is not just a convenient feature. It makes for greater reliability and also enables systems to withstand disasters. A process that is terminated can be started up immediately on another server, or even in another location.
Historically such usage models were limited because there were restrictions on ensuring the two physical machines that virtual machines were being migrated across to, had to be the exact same CPU family and generation.
This was because to guarantee both machines were capable of executing the exact same CPU instruction set. Intel FlexMigration is a technology built into the hardware that removes this barrier and ensures all future generations of Xeon are compatible with today’s existing generation.
In essence this makes the Xeon architecture future-proofed, says Crowe. "With Intel VT FlexMigration, you will be able to migrate your application onto any future Xeon processor, while it is still running."
Benchmarking virtual server performance
One way IT managers select the right server box for their needs is through benchmarking tests, which measure how well a server can run an application. But this has become more challenging in a virtualised world.
Currently there are several industry benchmarking initiatives to try and tackle this virtualisation challenge. Two of these are vmark and vConsolidate, developed by Intel and IBM.
The virtualisation benchmarks simulate a number of typical IT workloads including an email server, database server, web server, idle server etc. The server is then saturated by loading multiple workloads until performance deteriorates.
Virtual servers get users online quicker
But how well does it work in practice? To take one example, telecoms provider Telefonica was able to steal a march on rival operators and offer a virtual hosting service in Spain, based on Xeon's features. The company had offered its customers their own physical servers in data centres in Madrid and Barcelona, but moved to a virtualised model, where every customer gets dynamically-sized virtual machines to suit their needs.
Virtual servers can be launched quickly, instead of installing new hardware, so new customers can be up and running in a matter of days, instead of weeks and Telefonica is passing on hardware and power savings to its customers.
The service is delivered on 8-way servers from IBM powered by Intel Xeon 7100 series processors, upgradeable to 16-way servers. Telefonica runs VMware ESX, including Vmotion, so customers' virtual machines can be moved from one physical server to another, with no impact on end users.
The future of servers may be virtual, but the benefits are real - and virtualisation is built directly into the processors in today's servers.
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