vRanger offers or standard . Each of these replication modes has the option of ABM. VM replication in general starts with replicating the source VM to the target host. Changes are applied to the target VM at user designated intervals to keep the target in sync with the source. Thus the key difference between the replication modes is how vRanger identifies VM changes to replicate. For more information, see the following topics:
CBT tracks the disk block changes made by the source VM. When enabled on the source host, CBT records the blocks that have changed since the last replication pass and transfers them to the target host without scanning the VMDK. CBT only identifies these disk-sector changes when VMware® ESXi™ version 5.0 or later is installed on both of the hosts being used for replication.
NOTE: CBT must be enabled for each VM that you want to replicate. VMware vSphere® supports CBT, and most VMs running in this environment can use it.
In differential replication, vRanger compares the data blocks on the source VM to a data map to identify blocks that have changed since the last replication pass. These changed blocks are sent to the target VM and committed to disk, and the data map is updated to reflect the current state of both VMs.
• After the first replication pass, the source VM is scanned and the blocks are compared to the most recent data map. This scanning process can take an average of one minute per gigabyte of hard drive space; however, the actual speed depends on the underlying hardware being used. While only the changed data is sent to the target VM, the entire hard drive must be scanned. When configuring differential replication jobs for large VMs, take this scanning time into account. To eliminate the need for scanning, use replication with CBT if at all possible.
Replication transport actions occur through HotAdd — LAN-free or network. If one transport method is not available, vRanger attempts to perform the replication task using one of the other transport methods. You may configure the order in which vRanger attempts the transport options with the Transport Failover node of the Configuration Options page. For VMware® ESXi™ hosts, configure the transport order to VA-based HotAdd > VA-based Network.