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, 5 GB memory, 2 TB disk.

Our virtual servers are built using Linux KVM – the advanced virtualization plaform built into mainline Linux – which means that your virtual server is entirely independent of others on our farm and fully configurable by you to your needs, unlike solutions using only OS-level containers such as Virtuozzo/OpenVZ, which are used by many our our competitors.

Feature Description ElasticHosts Virtuozzo
Basic virtualization Run multiple virtual servers on physical hardware. Y Y
Full separation of virtual servers Rely on virtual servers having entirely independent and isolated environments for maximum flexibility and security. Y N
(same kernel)
Free choice of operating systems Run any operating system designed for PC hardware and any software on your virtual server. Y N
(limited to same OS as physical server)
Full kernel reboots Fully reboot your own individual virtual server. Y N
(user-space reboot only)

Correct at time of writing, 22 May 2008

Comparison with other virtualization technologies

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.