VM replication, as the name implies, is to create exact copies of the virtual machines, known as VM replicas. By continuously copy the running original VM, VM replication creates fully functional, ready-to-run VM replicas, provides the shortest recovery time objective (RTO).
Speaking of VM replication, you may think of VMware vSphere Replication, which was first introduced in VMware vSphere 5.1 Essentials Plus Kit as a built-in feature, and Hyper-V Replication, which was introduced in Windows Server 2012. This article will mainly illustrate VMware VM replication.
How does VM replication works for disaster recovery (DR)
According to different demands, there are 2 types of VM replication.
Real-time VM replication is to copy the data from original VM to the replica as it is written, providing the most accurate copy.
Point-in-time VM replication is to copy the data at scheduled intervals.
Normally the VM replica is stored in powered off state, and does not consume computing resources. In the event of a disaster, you can run the VM replica immediately and use it as the original VM, or copy the data from the replica to the original VM after it is repaired.
Therefore, VM replication significantly reduces disaster recovery (DR) downtime, and ensures business continuity.
Comparison between VM backup and replication
While both are necessary VM data protection measures, VM backup and VM replication are very different in working principle and purpose.
VM backup: The primary purpose is long-term storage. Therefore, VM backups preserve the VM data at the time of taking backup in a special backup format, and remove the duplicate and unnecessary data. To further save disk space for storing more VM backups, you can also enable data compression. When restoring from VM backup, you need a longer recovery time to restore the VM to the state it was in when the backup was taken.
VM replication: The primary purpose is to reduce the impact of the disruption from disasters. Therefore, VM replication copies the changed original VM data to a fully functional VM replica in real time or at the shortest possible interval, makes the VM replica is nearly the same as the original VM. In the event of a disaster, you can immediately run the VM replica to continue the business, reducing downtime costs.
How to choose from VM backup and VM replication
VM replication cannot replace VM backup. In a good DR plan, VM backup is required, but since VM replication is costly, you can decide if you need it based on your demand.
VM backup is cheaper, takes less disk space, and can provide you adequate recovery points for long-term storage.
Based on this, if you still need an accurate copy of the original VM, or if the DR downtime can result in greater cost than your budget, such as business loss, or damage to brand reputation, then you may need VM replication to create a VM replica.
For enterprises, combining VM backup and VM replication ensures almost absolute security of the VM data.
How to enable VM replication on vSphere
VMware vSphere Replication is a built-in feature on Essentials Plus Kit and higher versions of vSphere. It can be used with Site Recovery Manager (SRM). In this section, I will introduce how to install and configure vSphere Replication as demonstration.
How to install VMware vSphere Replication
1. Download VMware vSphere Replication Appliance from official site. Access to vCenter, right-click the host and select Deploy OVF Template… to deploy the ISO file as an OVF in your vCenter.
2. In Deploy OVF Template wizard, on Select an OVF template page, select Local file and click Browse… to select all the vmdk files and one ovf files you are going to use. Click Next to continue.
Note: To install vSphere Replication appliance (that includes Manager and Server), you need to select the files vSphere_Replication_OVF10.ovf. If is to install an additional vSphere Replication Server, select vSphere_Replication_AddOn_OVF10.ovf instead.
3. On Select a name and folder page, provide a unique name and location for the OVF. Click Next.
4. On select a compute resource page, select a host or cluster for vSphere Replication. Click Next.
5. On Review details page, verify the template details and click Next.
6. On License agreements page, accept the license agreement and click Next to continue.
7. On Configuration page, select the size of vSphere Replication Appliance as 2 vCPU or 4 vCPU.
By default, the deployment selects large 4 vCPU. You can select the smaller version if you have a small environment. Then click Next.
8. On Select storage page, select the VM Storage Policy and a datastore for vSphere Replication Appliance. Click Next.
9. On Select networks page, select a destination network for vSphere Replication Appliance and configure IP Allocation Settings. Click Next.
10. On Customize template page, you need to customize the deployment properties such as IP address, Gateway, DNS Name, NTP Server, DNS Server, and Domain. Click Next.
11. On vService bindings page, select the vServices to which the deployed OVF template should bind. Click Next to continue.
12. On Ready to complete page, review all the configurations and click Finish.
13. Access to https://IP-Address:5480 and enter the VAMI with the credentials. Click VR > Configuration to add LookupService Address and other information about your vCenter. Then click Save and Restart Service to start the service.
14. Do the upper steps on both 2 sites, then re-log in vCenter and click Menu > Site Recovery, you can see the Site Recovery is enabled.
How to configure vSphere Replication
1. Access to vSphere Web Client, navigate to Menu > Site Recovery and click NEW SITE PAIR to open the wizard, and input the information to connect to your target Platform Services Controller (PSC). Click Next.
2. On vCenter Server and services page, select the vCenter Server you want to pair. Then click Next.
3. On Ready to complete page, review the settings you selected, and click Finish to pair.
4. Click the site-to-site to login and input the credentials for the target vCenter, then you have access to it.
5. Right-click on the VM name from the left inventory and select All vSphere Replication Actions > Configure Replication… to open the Configure Replication wizard.
6. On Replication type page, select to Replicate to a vCenter Server, or Replicate to a cloud provider. Then click Next.
7. On Target site page, select the target site where the VM will be replicated. Click Next.
8. On Replication server page, you can choose Auto-assign vSphere Replication server, or manually Select vSphere Replication server at the target site that will handle the replication. Click Next.
9. On Target location page, Click Edit… and specify VM storage policy you created at the target site, to select a datastore where the replicated files will be stored. Click OK to back to the wizard, and click Next to continue.
10. On Replication options page, you can check Guest OS quiescing, and Network Compression options for the VM. Click Next.
11. On Recovery settings page, select the Recovery Point Objective (RPO) from 15min to 24hr, and enable Point in time instances. vSphere Replication supports the retention of up to 24 instances. Then click Next.
12. On Ready to complete page, review all the settings and click Finish to start VM replication. You can click Monitor > vSphere Replication > Outgoing Replications to check the replication status.
VM replication creates fully functional VM replica, allows you to continue your business right after the disaster. For enterprises, it can save the business loss, damage to brand reputation, and other costs caused by downtime.
