VMware: vSphere Replication Part 1 - Introduction

Today I decided to start a vSphere Replication blog post series in which I will cover replication functionalities offered by vSphere.

What is vSphere Replication?

vSphere Replication as name suggest is a replication appliance deployed in vSphere that allows VMs to be replicated between different datastores. Replication can occur within the same vSphere cluster managed by a single vCenter Server, or across clusters managed by different vCenter Servers.

A major benefit of vSphere Replication is the possibility to set RPO of VMs replication between 15mins up to 24hours, this means that in the worst case (assuming RPO of 15mins) you can loose up to 15mins of data.
Since replication can be performed on powered on VMs, and due to quiescing mechanisms involved during replication, more aggressive RPOs under 15mins were avoided since they could introduce performance problems in VMs quiesced too frequently.

vSphere Replication differs from standard array based replication by being hardware agnostic, no hardware prerequisites exist between source and destination storage, plus they don't have to share same communication protocol (i.e. iSCSI,FC,FCoE,etc.) to be connected neither they must be explicitly supported/certified for replication. It also differs from standard array based replication due to the fact that vSphere Replication can copy invidual VMs and not entire LUNs to destination array despite standard array replication offers an hardware offloaded transfer that does not contend for hypervisor's resources.

Another features is the support of replication seeds for VMs copying. Let's assume you have a VM with a 1.5TB vmdk disk. If you are replicating this VM over the internet sending to destination site 1.5TB may involve some time regardless of your internet connection speed. Replication seed allows to transfer this base vmdk using an out-of-band mechanism (i.e. transfer vmdk using an USB HDD) to destination datastore. Once replication is enabled on a VM with a replication seed vSphere Replication will notice vmdk already exists at destination datastore so it will transfer only changes occurred in VM disk using CBT evaluating source vmdk and destination vmdk.

How does it work?

vSphere Replication simply copies VMs from source datastore to destination datastore to meet configured RPOs.
VM at source site is quiesced and then whole vmdk, or delta-vmdk if base disk already exists at destination, is copied to target datastore.

vSphere Replication allows retaining point in time -PIT- copies of the VM that will be seen as VM snapshots once VM is recovered.

As said before vSphere Replication doesen't care if you are replicating VMs within same local site or across the network to a remote site managed by a different vCenter, all you have to do is properly configure Replication Server used by vCenter to connect to in order to set up replication.

vSphere Replication is available as a virtual appliance that comprises a vSphere Replication Management Server that provides replication management, a vSphere Replication Server that is in charge of performing actual data transfer between source and destination, an embedded database to store data and replication schedules, and a plug-in for vSphere Web Client that provides management capabilities for vSphere Replication within Web Client.

vSphere Replication can be managed only from vSphere Web Client.

Up to 10 optional vSphere Replication Servers can be deployed and managed by a single Management Server in order to provide replication load balancing. Up to 500VMs can be replicated from source to destination datastores.

How much does it cost?

vSphere Replication is included in vSphere Essential Plus or higher so it is "free" if you already purchased at least Ess+ license.


Other blog posts in vSphere Replication Series:

vSphere Replication Part 1 - Introduction
vSphere Replication Part 2 - Installation 
vSphere Replication Part 3 - Roles & Permissions
vSphere Replication Part 4 - Configuration
vSphere Replication Part 5 - Enable Replication  
vSphere Replication Part 6 - Perform Recovery  
vSphere Replication Part 7 - Provision additional Replication Servers