What Is vSphere Replication, and How Does It Work?

Creating and maintaining multiple virtual machines (VMs) at all the levels of the computing stack is a fundamental component of any modern IT infrastructure. Replication remains the most powerful tool that organizations can use to achieve performance, availability and mobility.

vSphere Replication(VR)—a feature first introduced in VMware vSphere 5.1—augments the recovery potentials of the vSphere platform. By continually replicating a running VM, vSphere replication allows organizations to not only improve performance but also enhance availability and mobility.

vSphere Replication Defined

vSphere Replication is an asynchronous, hypervisor-based VM replicator and recovery feature of the vSphere platform. As an alternative to storage-based replication, vSphere Replication can copy a VM to another site. Users can restore their VMs through the VMware vCenter Server and vSphere Web Client.

VMware provides vSphere Replication as a free feature for all the eligible vSphere platform licenses, including vSphere Essentials Plus, vSphere Standard, vSphere Enterprise and vSphere Enterprise Plus.

vSphere Replication has two main components: an agent (a core component of the vSphere installation package) and a set of vSphere Appliances that gets deployed from the vCenter management interface. The agent transmits the changed data from a running source VM to the target VM while the virtual appliances ensure that offline disk files in the remote VM receive the replication.

Also, the vSphere Replication Appliance helps manage the replication process, giving vSphere administrators the required visibility, they need to check the status of VMs, as well as restoring failed virtual machines.

For example, vSphere administrators can use the vSphere Replication Appliance to choose a Recovery Point Objective (RPO) that provides information regarding the age limit of VM copies. vSphere administrators can use this information to enforce policies that ensure that VM’s data do not expire for each replication configuration.

There are three ways that vSphere Replication can protect your VMs:

Replication between sites. In this topology, users must set up one vCenter Server at both the source and the target to manage the hosts. To allow replication between the sites, you need to deploy only one vSphere Replication appliance on the single vCenter Server. During the restoration process, you need to ensure that the target’s vCenter Server, vSphere Replication Appliance and other replication servers managing the replication process are up and running.

Replication within a single site. Unlike replicating between sites where there is one vCenter Server at both the source and the target sites, you have only one vCenter. However, the source must be different from the target datastore since you cannot use the same source and target datastores for the replication.
Replication from multiple locations to a shared target location. In this topology, you can use more than one vCenter to replicate to target sites. Alternatively, you can copy VMs to more than one vCenter. To replicate from multiple locations to a shared place, you must implement the vSphere Replication Appliance for each source and target vCenters.

vSphere Replication Features and Benefits

vSphere Replication removes many costly disaster recovery requirements due to its unique features such as:

It’s storage agnostic. Unlike most array-based replication techniques, vSphere Replication is independent of the storage technology and can work with any storage type, including the traditional storage area network (SAN), network-attached storage (NAS), virtual storage area network (vSAN) and direct-attached storage (DAS). Besides replicating VMs of the same kind of storage, you can also copy VMs from vSAN to DAS, SAN to vSAN, and SAN to NAS, among other types.
It has a flexible Recovery Point Objective (RPO). vSphere Replication provides an RPO between 15 minutes and 24 hours, which vSphere administrators can configure on a per–VM basis. Besides, administrators have the option of enabling multiple recovery points (point-in-time instances). This is a useful tool that can help organizations manage the recovery process for problems that get discovered only after several hours.
It replicates only the changes. After the initial and full replication of the VM to its target, VR ensures that only changes get copied to the target Virtual Machine Disks (VMDisks) using snapshots that save the recovery points. The snapshot approach ensures that the incremental copy gets applied fully to the target VMDisk. This allows vSphere administrators to preserve the old, known-good state of the target VM in case a problem arises during replication.
It has a simple virtual appliance deployment. VR Appliance leverages an Open Virtualization Format (OVF) file of the vSphere Web Client. When an appliance is deployed and powered on, administrators can use a web browser to access the Virtual Appliance Management Interface (VAMI) to complete the configuration process. There is no need to install or configure these components since they are already built into the vSphere platform, further simplifying VR deployment.
It supports Microsoft Volume Shadow Copy Service (VSS) and Linux File System Quiescing. VSS and guest file system quiescing provide a consistent interface for seamless coordination between the user and backup applications. This improves the reliability of the recovered VMs.

vSphere Replication Use Cases

Organizations can use VR to deliver flexible, reliable and cost-efficient replication solutions for data protection, disaster recovery and data center migration. Here are the details:

Data protection. Organizations can use vSphere Replication to transfer the contents of a data center to another site, either within the clusters or between the clusters, which are retrievable via the vCenter Server web-based interface. By replicating VMs through host-based and asynchronous incremental methodology, organizations can protect their VM on an ongoing basis.
Disaster avoidance and recovery. vSphere administrators can guard their data centers against disasters by copying them to other areas with VR, which augments replication crosswise over bunches and locales. Organizations can duplicate their data centers on the same vCenter Server instance, or to other Server instances inside the same location, across different sites and even via a VMware Internet-as-a-Service-based vCloud Air.
Data center migration. Migrating data centers between different sites may be a challenging undertaking for organizations that use conventional means such as script-based or manual approaches. VR, which is a proven real-time replication feature, can help such firms to ensure business continuity during the relocation process.

vSphere Replication Limitations

vSphere Replication offers clear benefits, but it also has some downsides. There are two categories of these limitations: VM Replication and vSphere Replication Appliance limitations.

VM Replication limitations

The virtual machines that you’ll deploy in a vSphere Replication environment can run into problems, such as:

Operational overheads. The snapshot technology employed by hypervisors to replicate VMs can create additional pressure on the organization’s production environment. Setting up too many VMs in the same replication environment may consume a lot of resources, potentially decreasing performance.
Bandwidth consumption. As is the case with any replication product, vSphere Replication must meet certain network requirements. For example, vSphere administrators must establish an organization’s dataset size, data change rates and RPO, and link speeds to allocate an optimal bandwidth that caters to these requirements. If not, the vSphere Replication product cannot achieve its goals.

vSphere Replication Appliance limitations

Within the vSphere Replication, the vSphere Replication Appliance has architectural shortcomings that include:

Each vCenter Server can only accommodate a maximum of one vSphere Replication appliance.
Each vSphere Replication Appliance can only replicate up to two thousand VMs.

Each vSphere Replication Server can only support two hundred VMs.

Parallels RAS – Your Ideal VDI Solution

vSphere Replication deployments are, by nature, complex and tedious. vSphere administrators must figure out not only the operational and bandwidth overheads involved with VR deployments, but also how to manage customer business expectations. In a business world that’s fast-paced and highly competitive, vSphere Replication—despite its potential benefits—may not live up to its promise.

Parallels® Remote Application Server (RAS) is an alternative for organizations that want a truly agile and scalable infrastructure to deploy enterprise-grade applications. The cloning techniques embedded in Parallels RAS simplifies the management of VMs in a Virtual Desktop Infrastructure (VDI) environment.

Parallels RAS uses the RAS VDI Agent—already installed in the Parallels RAS farm—to allow IT administrators to create and manage several VDI hosts from a single pane of glass. Once a single VM template is created, all the new virtual desktops update using the snapshot technology, thanks to the flexible cloning techniques inherent in Parallels RAS.

Parallels RAS supports many hypervisors, including VMware ESXi and Microsoft Hyper-V, and other hyper-converged infrastructures such as Scale Computing HC3, Hewlett Packard Enterprise (HPE) and Nutanix Acropolis to manage VMs. Parallels RAS has a simple and powerful interface that IT administrators can use to manage hypervisors via their native application programming interfaces (APIs).

Besides, organizations can leverage a single Parallels RAS solution to manage VMs from different hypervisors. This provides the flexibility and agility required in managing desktops and applications in today’s highly competitive business environments. Most importantly, Parallels RAS has the necessary security features that prevent unwanted access to VMs outside the use of clients.

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