It is evermore necessary to have a copy of production data which is being backed up on a regular basis to a local backup server repository. Sudden disaster might affect the backup server(s) leading to downtime and tedious productivity in a concern. In such cases, Replication is important as it is the act of synchronising data between a primary site and a secondary /Disaster Recovery site for the purpose of resilience. It is superior to backup since it focuses immensely on business continuity with a quick and easy resumption of operations even after a disaster.
A VMware ESXi host comprises several VMs. We usually store a copy of our VMs from an ESXi host to the backup server. All our VMs are backed up and the incremental backup schedules get triggered to the backup server.
What happens when the source ESXi host gets crashed?
VMware ESXi host may get crashed due to various reasons. It may be due to lack of network connectivity or host may become network isolated. If any host fails, all the VMs present inside that host will not function. So, it is always important to replicate backup VM(s) from source ESXi host to the another target host.
Merely, Virtual machine replication (VM replication) is a type of VM protection that takes a copy of the VM at that moment and copies it to another host. Whenever source host gets failed, VM(s) can be powered ON from the target ESXi host. A copy of the VMDKs to be replicated can be created and shipped to the target location.
Vembu VMBackup helps in easy replication of the VM from source ESXi host to a target host.
During VM replication between ESXi hosts, if different networks are used in the production site and Disaster Recovery site, it is mandatory to select the source and target networks configured whether it is IPv4 or IPv6 with dedicated network connectivity linking the production and recovery sites.
Re-IP mapping is to assign a new IP to the replicated VM. Re-IP rules are helpful if the IP addressing scheme in the production site differs from the DR site scheme.
You can configure a number of Re-IP rules for the replication job. When you perform failover, Vembu VMBackup Replication will check if configured Re-IP rules apply for the VM replica. If it applies, the VM replica will get a new IP address according to the new network mask, and you can reach this VM replica in the DR site.
User can perform Failover and Failback as a recovery process for replications.
Failover
Failover is a process that switches operations from original VM to its replicated VM on target host during a crash of the source VM. Once failover completes successfully, the replicated VM in target machine will be active and running. It has low RPTO and can restore in minutes.
During a disaster, target VM would be powered ON and further changes could be done on the replicated VM (i.e replicated VM could be used as the source VM in case of disaster), so called as Failover.
Failover will be finalised by any of the following operations
- Undo Failover
- Permanent failover or
- Failback
Undo Failover
This option is preferred when the source virtual machine is restored from a disaster or from a maintenance mode and activated successfully. In Undo failover, the changes done in replicated VM during failover session would be deleted and would revert back to its original state before failover.
Permanent Failover
Permanent Failover option makes the replicated VM as the source VM permanently. If the source VM is totally crashed or no longer recoverable, we would go for Permanent Failover.
Failback
After performing a successful recovery from the primary site to the secondary site, you can perform failback. Failback helps in recovering the failover data and creates a permanent VM. Virtual machines can be restored either to the same host or to the different host or can be restored in vCenter based on our necessities.
You could manually configure a new replication in the reverse direction, i.e from the secondary site to the primary site.
Finalize failback is enabled only when Failback gets completed. Finalize failback has two options. They are:
- Undo Failback
- Commit FailBack
Undo Failback
When a VM recovered as Failback does not operates properly or if the restore fails due to some reason, then Undo FailBack is used to revert back the replica to resume with the FailOver state. Again the user is allowed to select the Finalize Failover options if Undo Failback is carried out.
Commit Failback
When a VM performs its functions as expected after Failback, then Commit Failback option is chosen to confirm the VM to run separately. After Commit Failback is performed, VMs would be excluded from the replication schedules and none of the restore options could be carried out again.
Thus, VM Replication helps in copying (duplicating) and maintaining VM in another host especially in case of source host failure, enabling the business availability. It helps retrieving backed up VM from disastrous data loss.
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