Difference between VMware and xen
VMware vs xen:
With hardware getting more and more capable, by means of cheap multi-core processors and gobs of memory, we can expect virtualization to become only more important in the coming years. Virtualization promises reduced costs for IT organizations, both hard (machines, power, cooling) and soft (admin and operations personnel). There are lots of products on the market already, but two that draw the most attention are open source Xen and VMware family of products. Despite their popularity, there are ones who are still blind to the differences between VMware and Xen. Therefore, this article will provide a brief description on differences between VMware and Xen.
What is VMware?
VMware is a company that provides virtualization software for x86-compatible computers. VMware Inc. is a subsidiary of EMC Corporation and has its headquarters in Palo Alto, California. The term “VMware” is often used in reference to specific VMware Inc. products such as VMware Workstation, VMware Virtual Desktop Infrastructure, VMware Player and VMware Server. VM, which stands for “Virtual Machine” (not to be confused with the broader term virtual machine), is a widely-installed operating system for IBM-compatible computers and servers that can host other operating systems in such a way that each operating system behaves as if it were installed on a self-contained computer with its own set of programs and hardware resources. In 1998 VMware was founded by Diane Greene, Mendel Rosenblum, Scott Devine, Edward Wang and Edouard Bugnion. Greene and Rosenblum, who are married, first met while at the University of California, Berkeley. Edouard Bugnion remained the chief architect and CTO of VMware until 2005, and went on to found Nuova Systems (now part of Cisco). VMware developed a range of products, most notable of which are their hypervisors. VMware became well known for their first type 2 hypervisor known as GSX. This product has since evolved into two hypervisor products lines, VMware’s type 1 hypervisors running directly on hardware, along with their hosted type 2 hypervisors. VMware’s products predate the virtualization extensions to the x86 instruction set, and do not require virtualization-enabled processors. On newer processors, the hypervisor is now designed to take advantage of the extensions. VMware’s approach avoids some of the difficulties of virtualization on x86-based platforms. Although VMware virtual machines run in user-mode, VMware Workstation itself requires the installation of various drivers in the host operating-system, notably to dynamically switch the Global Descriptor Table (GDT) and the Interrupt Descriptor Table (IDT).
What is XEN?
Xen is an open-source virtualization solution. The Xen hypervisor acts as a thin layer between the hardware and the operating system, allowing multiple virtual servers to run simultaneously on a single physical server. Each virtual server acts independently of the others, with its own allocated area of RAM and virtual disks. Xen makes it possible for multiple guest operating systems to run on a single computer by using a software layer called a hypervisor to mediate access to the real hardware. The hypervisor acts like a traffic cop, directing hardware access and coordinating requests from the guest operating systems. Responsibilities of the hypervisor include memory management and CPU scheduling of all virtual machines (“domains”), and for launching the most privileged domain (“dom0”) – the only virtual machine which by default has direct access to hardware. From the dom0 the hypervisor can be managed and unprivileged domains (“domU”) can be launched. Xen, which was released under the GNU General Public License, was originally a research project at the University of Cambridge. XenSource, Inc., a company that supported the development of the open source project and enterprise applications of the software, was acquired by Citrix Systems in October 2007. Xen pioneered a form of virtualization known as paravirtualization, in which guests run a modified operating system. The guests are modified to use a special hypercall ABI, instead of certain architectural features. The Xen hypervisor is also exceptionally lean– less than 150,000 lines of code. That translates to extremely low overhead and near-native performance for guests. Xen re-uses existing device drivers (both closed and open source) from Linux, making device management easy. Moreover Xen is robust to device driver failure and protects both guests and the hypervisor from faulty or malicious drivers.
What is the difference between VMware and Xen?
XenServer, owned by Citrix, is based on Xen, but adds a complete GUI and other functionality similar to what you would find in VMware, such as storage virtualization. XenServer is less expensive than VMware, but it is far from free. When we refer to Xen, we are really referring to Xen, KVM, and any other built-in Linux virtualization engine controllable by libvirt, but not XenServer. VMware ESX Server’s architecture is based on direct execution (run user-level virtual machine code natively on the hardware) and binary translation (dynamically translate any privileged code). Since essentially a full x86 platform is exported to a virtual machine, ESX Server enables almost any OS that can execute on x86 to run inside a Virtual Machine (VM) without modification.Xen’s architecture uses a paravirtualization technique that modifies the guest OS so that it knows it’s running in a virtualized environment. With hardware-assisted CPU virtualization technologies like Intel VT and AMD-V, Xen 3.x also supports unmodified or fully virtualized guest OSs. VMware has also made announcements regarding paravirtualization support in its products. When talking about feature sets of VMware versus Xen, they are almost identical. Live migration (a horribly expensive “enterprise” feature in VMware) certainly works very well in Xen. Xen has supported live migration for years. Other fancy bits of VMware like storage pooling or storage virtualization are not part of Xen, because this is not Xen’s job. So, it is fair to say that VMware often wins the “integrated feeling” contest. This does not mean you cannot accomplish such things with Xen, instead it means that you’d use other functionality in Linux to accomplish them. It certainly is more DIY. Xen, however, focuses on features and performance of virtualization. That core functionality is constantly being improved and tweaked, and because they aren’t worrying about point-and-click features, the focus is in the right place and yields amazing results. VMWare is also capable of accepting more powerful hardware compared to Xen.
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