With vSphere Replication, formerly known as host-based replication, you can now copy virtual machines (VMs) from one storage type to another (e.g., from a local Virtual Machine File System data store to a Network File System volume) without any regard for the storage vendor or protocol.
Previously, storage array-based replication was the only way to move large amounts of data offsite. Because of the associated equipment and licensing costs at both the primary and secondary sites, only the largest enterprises could afford it for their disaster recovery storage.
VSphere Replication, on the other hand, lets you use cheaper disaster recovery storage at a secondary site. So once you get past the technical aspects, it’s a boon to small and medium-sized businesses (SMBs).
VSphere Replication: Tech specs
VSphere Replication sits above the vSphere host’s storage layer, which makes replication of VMs between different storage types possible. It consists of three components:
- VSphere Replication Management Server. This virtual appliance handles setup and
configuration. VSphere Replication Management Server is registered with vCenter Server and
stores your configuration in a back-end database. It supports databases found in VMware’s support
matrix, including flavors of Microsoft SQL Server, Oracle and DB2.
- VSphere Replication agent. This component resides in an ESXi 5 host and looks for
changes in the virtual disks that are marked for protection. The agent then sends the changes to
the recovery site.
- VSphere Replication Server. This appliance is located at the recovery site and receives the delta-based updates from the protected site.
It’s possible to have a vSphere Replication Server appliance and a management server appliance at both the protected and recovery site for two-way protection in an active-active, or bi-directional, setup.
The pros of vSphere Replication
For many years, all but the largest enterprises have been shut out of the replication market because of the prohibitive costs of having matching storage arrays at two sites. Many storage vendors, such as EMC Corp. and NetApp Inc., also sell array-based replication as a licensing add-on, so interested users are forced to buy both hardware and licenses.
VSphere Replication is ultimately a cheaper way of achieving the same protection that large corporations have enjoyed for years. Of course, there are other tools that provide similar capabilities, such as Quest Inc.’s vReplicator, Veeam Inc.’s Backup and Replication, and the newly minted Zerto Hypervisor-based Replication. But vSphere Replication will most likely be the only system that fully integrates with vCenter Server and Site Recovery Manager (SRM).
VSphere Replication may also alleviate the complexities of integrating multiple arrays with varying firmware levels at different sites. It sits above the storage layer, so the underlying hardware doesn’t matter.
In addition, vSphere Replication can also help circumvent the compatibility issues that arise when corporations reserve tier-one storage for production environments and deliberately select lower-level disaster recovery storage to keep costs down.
The pitfalls of vSphere Replication
Despite all these benefits, vSphere Replication is not without its challenges. Only certain features are supported when it’s used in conjunction with SRM. For example, vSphere Replication does not support SRM’s new automated failback feature, which is a recovery plan that reverses a failover back to the primary site.
VSphere Replication users also won’t have access to Reprotect Mode, which automates many of the manual steps necessary for failback. But the absence of Reprotect Mode may not be the end of the world, because previous SRM customers had to manually invert the failback process with array-based replication for years.
Another issue to consider is that vSphere Replication is not a core vSphere 5 feature. Instead, it’s shipped in a separate SKU with SRM. Ideally, VMware will offer a cost-effective price point for SRM to attract SMBs and small enterprises, but at the moment, it remains to be seen.
Some will say that shackling vSphere Replication to SRM is a deliberate attempt by VMware to up-sell customers, and there may be some merit to that statement. After all, VMware is not charity. But I would argue that replication (vSphere Replication) without automation (SRM) misses the point -- especially if you’re moving an entire data center during the disaster recovery process.
This was first published in July 2011