Numerous virtual private server (VPS) options are available for the enterprise, each with its own unique strategies,
techniques and configurations. It's hard to distinguish among them without some understanding of the fundamental concepts behind each technology. It's also difficult to evaluate the competitive advantages of each VPS solution in comparison to the rest of the field. This article briefly examines differences between two similar products from the same vendor, Virtuozzo and OpenVZ from SWsoft.
SWsoft's Virtuozzo and OpenVZ products cater to different crowds in the same market space. They also make possible an excellent side-by-side comparison of proprietary and open source features. But let's first review the leading methods for server virtualization.
- Virtual machines (VMs) emulate system resources running on host resources and create a Guest operating system (OS) environment for each targeted platform. Subsequent OS images execute within a guest OS container without modifying the underlying OS. This, in turn, requires a VM monitor (VMM) to validate all guest-issued CPU instructions.
- Paravirtual machines (PVM) also require a VMM, but the primary difference is that any guest OS must be modified to work within a PVM volume. The OS itself must be designed to utilize privileged system calls sparingly, and each instance must be uniquely identified to operate alongside other guest operating systems.
- Virtualization from the OS point-of-view is more intrusive to kernel source code but gains the ability to operate several instances of a single OS and provides greater isolation for concurrent applications or OS execution threads. Instead of using a guest/host paradigm, OS-level virtualization logically subdivides existing resources so that other OS instances can coexist within well-defined boundaries.
Virtuozzo abandons the typical hardware abstraction layer constructed in guest emulation environments to adopt a method for subdividing resources logically and according to administrative policy. On the Linux side, Virtuozzo runs a single Linux kernel as its core and exports that core functionality to various distributions, each of which effectively becomes a stand-alone entity. Each virtual private server (VPS) instance created on a single host has a separate set of login credentials, system processes, daemon services and network address, and can function as a template for rapid deployment of other virtual private servers. Keep this in mind as you peruse the cursory evaluation of proprietary and open source products that follows.
OpenVZ is a subset of the Virtuozzo platform and a test bed for future development of the commercial product line. The OpenVZ platform supports eight 32- or 64-bit CPUs, 64 gigabytes of RAM and a maximum of 100 concurrent VPS instances. Without being restarted, a single OpenVZ host can scale dynamically between minimal and maximal system resources according to increased demand. Furthermore, OpenVZ uses a single version of the underlying Linux kernel for each of its VPS instances while also enabling separate distributions to run concurrently. This makes OpenVZ ideal for early-adopters, custom in-house integrators and small IT shops in which physical resources are used conservatively but also require support for a variety of Linux distributions.
On the commercial side, Virtuozzo targets production environments and increases the scalability, performance and range of utilities included. All this added functionality facilitates improved management and utilization of virtualized resources. Virtuozzo runs on both Windows and Linux servers, unlike OpenVZ with its direct tie-in to Linux core components. As a for-a-fee product, Virtuozzo boasts a more robust feature set than OpenVZ, including support for up to 32 processors using 32-bit or 64-bit x86 architectures and thousands of managed virtual private servers. GUI and browser-based management tools facilitate administration, monitoring and provisioning of VPS resources in Virtuozzo.
The Virtuozzo Management Console (VZMC) is a client-level management console that provides consolidated access to remote VPS management for both Windows and Linux hosts. This console facilitates configuration, maintenance and patch management for these platforms. It deploys quickly across all VPS instances. The Virtuozzo Control Center provides remote management and consolidates all the functionality of its various console management applications.
Virtuozzo has a clear and present advantage over OpenVZ for large scale enterprises, especially those that use both Windows and Linux platforms. Virtuozzo works especially well for situations in which multi-processor scalability is a factor. It can also play a significant role in high-density server deployments, thanks to the wide variety of server management facilities it includes. OpenVZ is best suited for VPS populations that number in the hundreds or for situations in which in-house platform development efforts revolve primarily around one or more Linux kernel versions.
Justin Korelc is a long-time Linux hacker and system administrator who concentrates on hardware and software security, virtualization and high-performance Linux systems. Ed Tittel is a full-time freelance writer based in Austin, Tex., who specialized in markup languages, information security, networking and IT certification. Both Justin and Ed have contributed to books on Home Theater PCs and the Linux-based MythTV environment, and they write regularly about Linux for several TomsHardware sites.
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