Infrastructure

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ElasticHosts virtual servers come in sizes to suit all businesses, from a basic, but fully capable server from £29 per month to high-end configurations with up to eight cores, 8 GB memory, 2 TB disk.

Our virtual servers run on our sophisticated server farms, located two fully-independent premier-class data centres near London in the UK. We monitor, service and upgrade the underlying infrastructure, providing you with high availability and the capacity to scale up rapidly.

Our virtual servers offer all the power and control of a traditional hosted server, whilst giving you the benefit of:

• Instant flexibility: to scale your machine up or down using any web browser
• Peace of mind: of running on professionally managed infrastructure, with automatic failover
• Cost efficiency: of buying exactly the capacity you need on an infrastructure built to scale, and growing only when you need to

The technical details

Each layer of our infrastructure has been carefully designed and configured by our team to provide optimum performance to your virtual servers. We have deep understanding of this entire stack, and have contributed to the development of many of the software packages which we use in order to add features which we needed to provide you with our flexible, scalable and efficient service.

• Virtual server environment: you have complete control to choose the operating system, applications and configuration of your machine, just like a physical hosted server. In addition, you can use any web browser to scale your machine up or down and to manage all of the full suite of services that you need for your web application (e.g. domain registration, DNS).
• Virtualization platform: we use Linux KVM, the advanced virtualization platform built into mainline Linux. As described below, we believe KVM is superior to Xen, VMWare and Virtuozzo.
• Clustering technology: we cluster our servers for redundancy, load balancing and automatic failover, using RAID to keep your data safe and your virtual server running even in the (unlikely!) case of hard disk failure.
• Server OS: we run our own stripped-down Linux distribution on our servers to host the virtualization platform with maximum efficiency and security.
• Server hardware: we use high-end multi-processor servers, fitted with quad-core AMD "Barcelona" Opteron CPUs (B3 revision). These are the first processor released by either AMD or Intel to offer second generation hardware support for virtualization, greatly increasing performance and effectively eliminating MMU virtualization overhead.
• Network connectivity: we connect via Peer 1's high performance 10 Gbps SuperNetwork and Connexions4London's Multihomed IP Transit.
• Data centres: we operate two completely independent UK availability zones, located with Peer 1 in Fleet and BlueSquare 2 in Maidenhead, both near London.

Why we chose KVM virtualization

Before selecting Linux KVM, we evaluated VMWare and Xen, two other virtualization platforms providing similar capabilities to KVM (Virtuozzo only provides OS-level containers). We selected KVM as the best architecture for virtualization on modern processors with fast hardware virtualization support (VT-x and NPT on Intel or AMD-V and EPT on AMD).

Increasing hardware virtualization support

• Historically, virtualization platforms used software to trap and simulate certain instructions, memory management and I/O in the host virtual machines. VMWare was an early leader in this software technology.
• With the first generation of hardware virtualization, the VT-x/AMD-V extensions trapped these instructions in hardware, giving a significant speed improvement. However, virtualized memory management and I/O remained bottlenecks. Xen was an early proponent of paravirtualization, which attacks those bottlenecks by modifying the host operating system at compile time.
• With the second generation of hardware virtualization, the NPT/EPT extensions minimize the memory management bottleneck. As a result, MMU paravirtualization is a legacy approach, leaving just scheduling and I/O to be virtualized in software by a hypervisor. (I/O virtualization requires a good set of device drivers for the underlying hardware, of course: an area in which Linux excels.)

Hypervisor architecture and device drivers

• Linux KVM is a hypervisor which is built into mainline Linux. It uses the full range of hardware virtualization support, and directly uses the regular Linux scheduler and I/O device drivers.
• Xen runs an external hypervisor for scheduling, and uses a modified Linux kernel in domain 0 to provide device drivers.
• VMWare runs a proprietary external hypervisor, which includes scheduling and device drivers, many of which are adapted from Linux.
• We believe the KVM architecture is superior to both Xen and VMWare, since the mainline Linux scheduler and device drivers are both extremely well designed, widely deployed, professionally maintained and throughly tested, to a level likely well above what a single company can achieve on either their own proprietary codebase or locally maintained fork of Linux.