A bare metal hypervisor (aka "Type 1 hypervisor") is desktop virtualization software that can be installed onto your personal computer's hardware, i.e., the "bare metal" components of a PC's hardware. Bare metal hypervisors control at least one guest operating system as well as the hardware and can be combined with management tools to facilitate distribution of updates and patches. In addition, a Type 1 hypervisor can replace desktops if they are damaged and eliminate lags in performance produced by latency. Type 1 Hypervisors vs. Type 2 Hypervisors Instead of being installed on computer hardware, Type 2 hypervisors operate within a machine's host operating system, which permits a guest OS to run as a third stratum above the indigenous OS and the hypervisor. Additionally, Type 2 hypervisors create VMEs (virtual machine environments) by coordinating calls for memory, network, CPU and other resources via the native operating system. In contrast, Type 1, "bare metal" hypervisors do not need a host operating system to function properly because it can directly access the elemental physical hardware. However, regardless of how they are implemented, guest operating systems and virtual machines are usually unaware of the kind of hypervisor being utilized, since they communicate exclusively with the hypervisor. Why Use Bare Metal Hypervisors? Two popular, solution-based bare metal hypervisors are the Citrix XenServer and VMware ESX(i), Both offer the versatility afforded by Type 1 hypervisors as well as security enhancements such as a hypervisor's capacity to eliminate vulnerable OS attack surfaces. Since bare metal hypervisors support the operation of systems-insulating "bubble"-type environments, infections and other malware can be deleted without compromising a hypervisor's integrity. Features of the VMware ESX(i)
Designed to establish servers as computing appliances, VMware ESX(i) also allows for installation on a dedicated storage device so that it operates less like traditional software and more like firmware.
Management and monitoring tasks can be completed via application programming interfaces (APIs), which used to be done via service console tools.
Administrators can troubleshoot and rectify abnormalities on VMware ESX(i) hosts using tech support mode's command interface (shell). This applies primarily to exceptional issues that can't be managed remotely, such as break/fix schemes.
Scriptable installations are fully supported; users can also run scripts that have been installed before and after, including configuration of post-installed configuration scripts using vCLI or PowerCLI.
A smaller version of ESX, VMware ESXi is defined by the VMkernel OS and is available without having to purchase a vCenter license. ESXi is a free download but the free version lacks certain features, such as the ESX service console.
VMware recently released a new version of its ESXi hypervisor offering, among several other items, numerous bug fixes described in VMware's Resolved Issues document and support for external databases including Microsoft SQL Server 2012 and 2014.
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Features of the Citrix XenServer
XenServer allows users to incorporate more than one Xen-enabled server for creating a purposive resource pool that utilizes common storage frameworks while powering resource-aggregating technology developed by XenSource.
By seamlessly virtualizing multiple servers into a dynamically controlled resource pool, Citrix Xen Server delivers availability, resiliency and the optimal integration of information center resources. IT managers can also manage resource pool clusters from one access point so that simultanteous reductions in complexity and cost are achieved.
XenServer maximizes advantages of automated testing and development of software, protecting production loads sensitive to performance appraisals and automatic resource assignment tasks.
Modification of guest OSs through XenServer's paravirtualization technology that provides almost classically native performance. However, Xen does support OSs that are unmodified by relying on processor extensions (AMD-V and Intel VT).
Supports 64-bit and 32-bit processors regardless of whether a physical address extension exists. Xen also supports symmetric multiprocessing guest OSs.
For LInux VMs, Xen can reuse Linux device drivers already installed while remaining robust during device driver failures.
Precise resource partitioning provided for network I/O, block memory, and the CPU improves security by protecting drivers and VMs from denial of service attacks. Security is also tested continuously and remains open to examination by Xen's security community.
XenServer has live relocation capability (XenMotion) that allows VMs to be moved to other servers while running in the event that a XenServer host requires physical maintenance. Additionally, XenMotion's technology results in negligible delay during the relocation.
Available in Platinum, Enterprise, and Advanced editions, XenServer is also available as a free download (offers only basic virtualization functionality) and as a trial download that features all XenServer benefits for a limited time.
Primary Differences Between VMware ESX(i) and Citrix XenServer
Although they are both bare metal hypervisors, ESX(i) and XenServer virtualize differently in regards to using disk formats, APIs, interfaces, and licensing applications.
VMware is slightly more expensive but it can run more VMs with identical machine specifications.
VMware is also a bit faster than XenServer on most OSs, especially when it is used on a Windows platform, where Xen scores lower on speed.
XenServer uses its paravirtualization technology to modify its current OS. Alternately, VMware does not need modification because it uses binary emulation and translation. Consequently, installation and management of VMware may be moderately simpler compared to Xen.
XenServer software also requires AMD-V or Intel-VT hardware, which means Xen users will have to upgrade if they have incompatible hardware. VMware does not present this issue and can run on any hardware that meets its requirements. Moreover, VMware is capable of integrating more robust hardware than Xen is capable of accepting. This makes VMware adaptable enough to simulate more machines implementing one system. If you are interrested on reading more on VMware, I recommend that you have a look at this article on the advantages of using VMware.
