By Vissarion Yfantis

November 7, 2019
Last updated on July 8, 2022

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Citrix Hypervisor, Its Role in VDI Solutions and Possible Alternatives

What is Citrix Hypervisor?

As its name implies, Citrix Hypervisor is a hypervisor—a software component that separates the operating system and applications from the physical hardware. It’s able to run multiple guest operating systems and applications, commonly known as virtual machines (VMs), on one physical host. The hypervisor manages and presents hardware resources like RAM, CPU, and storage to each VM and acts as if it were the underlying hardware.

This hypervisor is, more specifically, a Type 1 hypervisor. In other words, unlike Type 2 hypervisors, which run on top of conventional operating systems (which in turn also run on physical hosts like Hyper-V), it runs directly on bare metal, i.e., the physical hardware itself.

How Citrix Hypervisor Works 

There are several components involved in delivering Citrix Hypervisor functionality. The key components are: 

• The Hardware Layer: It includes the physical server components, like CPU, memory and disk drives. To run all guest OSes supported by Citrix hypervisor, you must have an Intel VT or AMD-V 64-bit x86-based system with at least one or more CPUs. 
• Xen Project Hypervisor: Citrix Hypervisor is based on Xen Project Hypervisor and has few additional features by Citrix. It is an open-source type-1 hypervisor that allows many OS instances to run simultaneously on a single host.  
• Control Domain: It is a secure, privileged Linux VM that runs the Citrix Hypervisor toolstack, or XAPI. It instructs the hypervisor to start or stop guest VMs and provides all management functions. It also runs the device drivers, such as storage and networking.  
• Toolstack or XAPI: It is a software stack that provides management of Citrix Hypervisor resources pools and controls VM operations and functions like user authentication and VM storage and networking. It also provides the management API that is used by other tools managing VMs and their resource pools. 
• Guest Domain (VMs): These are virtual machines created by users that request resources from the control domain.  
• Citrix VM Tools: They provide high-performance I/O services between the VM and the Citrix hypervisor.  

Formerly known as XenServer

Some time ago, Citrix Hypervisor was known as XenServer. “Xen” is the name of the hypervisor technology first developed by the University of Cambridge and eventually improved by Citrix. Here’s the history of that process:

Sometime in 2003, about a year after the original Xen was publicly released, the main developers founded XenSource. XenSource was formed to market Xen as an enterprise product. However, in 2007, the company was acquired by Citrix. Citrix retained ‘Xen’ in its branding and named its Hypervisor XenServer. Citrix XenServer was then rebranded in early 2018 as part of Citrix’s unification plan to rename the majority of its flagship products.

Citrix Hypervisor vs. VMware Hypervisor

Both Citrix Hypervisor and VMware Hypervisor perform similar roles, however, with notable distinguishing features. The table below summarizes the primary differences between Citrix Hypervisor (whose current version is 8.2) and VMware Hypervisor (currently, VMware ESXi version 7.0).

Compute

Memory

Storage

Networking

Software

Changes in Citrix Hypervisor LTSR

Citrix Hypervisor 8.2 was released three years after the XenServer 7.1. Here are a few additions and changes that were introduced between the two LTSR versions.

• LTSR allows admins to conveniently work with the familiar environments by providing extended lifecycle and support for the same version of Citrix Hypervisor and Citrix Virtual Apps and Desktops. Admins don’t have to update components frequently.
• Citrix Hypervisor 8.2 LTSR has shifted to an updated CentOS userspace and the latest Xen, enabled by the new Linux kernel.
• The new LTSR version has increased the pool size from 16 hosts to 64 hosts, and it handles complex configurations more efficiently. Admins have to manage fewer pools for the same number of hosts. The High Availability plan computation feature dynamically constructs a failure plan based on the events impacting a specific pool.
• The next-generation XenCenter facilitates IT admins by allowing updating multiple pools simultaneously, enhanced licensing visibility, performance improvements and much more.
• XenCenter now allows admins to replace the Citrix Hypervisor host TLS certificates and also alerts the admins when the certificate nears expiration.
• Admins get further granular control by scheduling snapshots on a single or multiple VMs. They can configure the maximum number of snapshots which will automatically keep deleting the oldest ones.
• It supports SR-IOV to achieve optimal I/O performance by allowing VMS to communicate directly with the network adapter through Direct Memory Access.
• It supports Guest UEFI and Secure Boot to further strengthen security right from the boot process by verifying OS signatures against Microsoft’s public keys when the system boots.
• Citrix Hypervisor supports AMD, Intel and NVIDIA for delivering high graphics workloads. The new LTSR version has a vGPU live migration feature which allows VMs to be redistributed when running out of host resources. It also supports multiple vGPUs on a single VM to enhance app performance and expedite workflows.

Parallels RAS: An All-in-One VDI Solution

Parallels® Remote Application Server (RAS) is a virtual desktop infrastructure (VDI) solution that enables businesses to publish applications, desktops, as folders and data, to any device. One of its key features is the ability to publish VDI desktops, which are virtual desktops hosted on virtual machines. These VMs are in turn hosted on hypervisors like Microsoft Hyper-V.

Parallels RAS supports most major hypervisors including hyper-converged technologies, including Microsoft Hyper-V, VMware ESXi, Scale Computing HC3 and Nutanix Acropolis. This flexibility reduces the barriers to entry for companies who wish to adopt virtual application and desktop delivery while also helping them avoid vendor lock-in. In addition, Parallels RAS supports multiple hypervisors under the same infrastructure, which provides the flexibility of leveraging existing or different infrastructures from a single pane of glass. If you’re looking for a Citrix alternative, Parallels RAS one worth mentioning.

Try your 30-day evaluation period of Parallels RAS and leverage multiple hypervisors!

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