Parallels Virtuozzo Containers

This page contains a technical information on Parallels Virtuozzo Containers, the virtualisation software we use to power our Linux VPS products. Even more information is available from www.virtuozzo.com

Virtuozzo Overview

Parallels Virtuozzo Containers is an operating system level server virtualisation solution - it creates isolated partitions (known as Containers, Virtual Environments or Virtual Private Servers - VPSes) on a single physical server and OS instance to utilize hardware and software with maximum efficiency. Indeed, Virtuozzo’s OS virtualisation solution has higher efficiency and manageability than most competing technologies.

Virtuozzo works by adding a single "thin" layer to an existing host operating systems to allow for the creation of the isolated partitions (each able to run its own flavour of Linux) on top of the common OS. The Virtuozzo layer introduces only a small overhead, which results in better performance per VPS compared to running the same number of VPSes on the same physical server under competing virtualisation technologies.

Each VPS appears to its users and administrator to be, to all important intents and purposes, a full physical server. Each VPS can run its own flavour of Linux (Centos, Red Hat, Fedora, Ubuntu, Debian etc) has its own processes, users, files, root or administrator access, full networking, system libraries and basically everything it needs to appear to be a standalone server.

Interestingly, no matter how many VPSes make use of it, there will only be one "master" set of operating system files installed on the physical server for each flavour of Linux used. Each VPS initially just contains symlinks back to these master files. The use of these symlinks make a VPS's initial footprint extremely small, since a full set of OS files do not have to be stored for each one. Any changes you make to the OS files -- replacing them with different versions, for example - are then stored in a private area on the physical server that is only accessible to your VPS. All this happens invisibly, of course, with the VPS itself only seeing a single, normal file system that appears no different to that on a real physical server.

Another interesting situation arises when multiple VPS users run exactly the same versions of a particular application and associated modules - for example the Apache web server. In such a situation, only one instance of the core code will be loaded in memory on the physical server. This means that a VPS may not need as much memory allocated to it to run a particular application than would be the case with the same application running on a physical server.

Complete Isolation

Complete isolation ensures that the VPSes are secure and have full functional, fault and performance isolation. This is achieved through multiple layers of security designed to ensure that each VPS is secure, isolated and unaffected from other VPSes on the same physical server.

Virtuozzo’s patent-pending technology, Kernel Service Abstraction Layer (KSAL), mediates activity to the kernel and prevents any single VPS from taking the entire server down. Virtuozzo File System (VZFS) is a proprietary file system (invisible to the VPS user) that, ensures that a user cannot access any other VPS or part of the server.

Dynamic Resource Allocation

Dynamic resource allocation of key system resources such as CPU, memory, network, disk and I/O enables us to achieve near real-time changes without affecting a VPS or its workload. Virtuozzo’s sophisticated resource management controls CPU, memory, network I/O, disk space and other system resources.

Virtuozzo assigns, monitors, accounts and controls resource levels in real-time and alerts administrators and users according to pre-defined criteria. Should adjustments in resources be required, we can very easily change the resources in real-time. A unique feature of Virtuozzo resource management is the ability to “burst” or allow VPSes to use resources that are currently unused on the server. In this respect, a VPS can get at least its guaranteed resources on the server.

How is Parallels Virtuozzo Containers Different?

You may be wondering how Parallels Virtuozzo Containers OS level virtualisation compares to the competing hardware virtualisation technologies such as VMware, Xen and Virtual Server?

With the hardware virtualisation technologies, above the hypervisor or virtual machine monitor level is a virtual hardware level. In order to assign resources, this type of technology must virtualise every single piece of hardware, in essence recreating the work of the hardware vendors and the OS software vendors that already support the hardware. Finally, inside the guest virtual machines, there is a complete copy of an additional operating system and the residing workloads or applications.

Such hardware virtualisation has its benefits. At least on the leading market solution, just about any operating system is supported in the VPS and it is possible to run Windows VPSes on the same physical server as Linux and Solaris VPSes. This isn't possible with Virtuozzo which only allows Linux VPSes to be created on a physical server whose base OS is Linux (or only Windows VPSes on a physical server running Windows).

Despite the benefits, the flexibility of this type of solution comes with a lot of overhead and inefficiencies.

• A single application has two OSs to traverse; the guest-level OS and the hypervisor or host OS. More processing equates to slower responses and more overhead.
• Each OS takes space in memory, and memory is always the most constrained resource on a server. While some vendors have taken steps to maximize memory usage, the inefficiencies still exist.
• The use of complete duplicate OSs for each VPS consume hard drive space and must be licensed and managed separately, resulting in higher costs.
• Hardware support and interoperability for all of the hardware on the market is difficult to emulate well, so it is often a source of slower response times and higher processing overhead.

As an OS-level virtualisation solution, Virtuozzo uses a single standard Operating System on a server. This model eliminates the inefficiencies of hardware virtualisation

Performance

• Parallels Virtuozzo Containers uses all of the real hardware and OS software. There are no rewritten drivers or OS technology. There is also very little or no delay in supporting new technologies and it performs at near-native server levels.
• There is no duplicate OS, so it again performs very efficiently.
• Because of the near native server performance, Parallels Virtuozzo Containers is used to virtualise high I/O applications such as data bases and email servers.
• System Calls: Parallels Virtuozzo Containers has a common kernel, no additional systems calls are created between excess layers.
• File system: Common data is stored only once and is available to multiple environments, significantly improving the efficiency of both the disk space and system memory. The disk space for caching is also used efficiently, caching payload rather than duplicated data.
• File system buffers/cache in memory: Parallels Virtuozzo Containers places a single instance of data and cache across the server, maximizing memory efficiency.

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