Alike v6/A2 Documentation

Welcome to the Alike documentation

Replication Overview

A2 Alike replication offers an efficient and high-performance way to copy virtual machines from one hypervisor to another. Alike replicates a source machine to a target destination. Alike requires that the source host be licensed. The destination host does not need to be licensed.

Enhanced vs Q-Hybrid

Alike features two basic replication modes: Enhanced (Agentless) replication, and Q-Hybrid (Agent-Based) replication.

Enhanced Replication

Enhanced replication uses Alike agentless backup technology to replicate a VM from XenServer to XenServer or from Hyper-V to Hyper-V. If you wish to replicate across hypervisors, you must use the Q-Hybrid method.

XenServer enhanced replication uses ABDs to perform XenServer snapshots, create delta sets between source and target, and send data. You must have your ABDs correctly configured on both source and destination environments in order for replication to function. Please see XenServer Configuration for more information

Data is sent over port 2811, although you can change this setting under Alike Settings->Network Settings.

Hyper-V Enhanced replication connects to the hyper-V host and runs Windows executables remotely on the hosts in order to take snapshots, calculate deltas, and send data.

CBT Enhanced Replication

CBT replication is a way of accelerating replication performance by dramatically reducing amount of data that must be read off the source VM. This is done by only reading changed data using a delta with the previous snapshot. CBT replication requires a snapshot to be maintained on the hypervisor between replication runs, and therefore will cause some amount of storage overhead.

CBT replication does not use ABDs on XenServer. Instead, it copies delta information to and from the source and destination using your ADS as intermediary storage, and then deletes this data after the replication completes. You will need free space on your ADS equal to the size of the VM's full export in order to complete the initial pass. After this, space requirements will be based on the amount of delta data discovered.

Q-Hybrid Replication

Q-Hybrid replication uses a temporary agent within the target VM. This agent takes a VSS snapshot of the machine's volumes and performs delta and data send. In order to use Q-Hybrid, you must first set up ancredential profile in the Alike UI. See our section on backup for more information.

Note that replicating a gen2 hyper-V VM to XenServer will likely result in an unbootable replica. While your data will be intact and valid, XenServer does not support UEFI boot, only BIOS, and therefore will not be able to start up your VM.

Physical Replication

Owners of Alike Physical licenses can replicate a supported Windows physical machine to a virtual machine target running on either Hyper-V or XenServer. Alike uses its Q-Hybrid replication technology against all physical replication targets. Alike ensures your volumes are replicated faithfully, but cannot assure the bootability of the resulting VM in all cases.

Single-Pass Backup and Replicate

Single-pass backup and replicate allows you to replicate a VM to a target and take a backup at the same time, with only one snapshot being taken. Furthermore, the source disks are only read once. Single-pass backup and replication does not support CBT.