Replications On A Theme - Host-Based Replication

Disaster recovery is certainly more than getting the data out of your data center and having it land in a remote facility, but that isn't a bad pace to start. Problem is, there are now 800 different ways to replicate data.I typically break these down into three areas; host-based replication, appliance-based replication, and storage controller-based replication. I'll dive into all of these over the next few blogs, but suffice to say, you have options.

First up is host-based replication. I'm not sure whom to give credit to for this space, but the guys that come to mind most often lately are DoubleTake Software and SteelEye Technology. Host-based replication installs an agent on each server that you want to protect, all managed by a central console.

Sometimes I think that host-based replication has been forgotten in the rush to networked storage, but it continues to be very viable in certain situations. For example, in smaller accounts that simply don't yet need a SAN but have mission-critical information, these are very cost-effective solutions to getting that done.

Second, staying with the small-business theme, if the business is also using server virtualization, then these solutions also give you some capabilities as it relates to virtual server migration. Virtual machine migration normally requires shared storage. This is the ability to move a virtual machine from one physical host to another physical host. With some of the host-based replication solutions, you can pull this off without networked storage -- just replicate from one internal hard disk to another.

A viable solution is to have a two-server environment with two internal drives each. Each primary drive could replicate to the secondary drive in real time. This covers you from a basic drive loss situation and sets the stage for virtual migration. When the need arises to move a virtual machine, you could stop the replication and move your virtual machines over to the alternate server. The reasoning behind this could be a simple need to load balance or to perform maintenance on the first server.

A final situation applies to even large environments. Large environments have two situations that make using host-based replication a nice complement to storage-based replication. First, most larger data centers don't have only one SAN. Replicating from brand A to brand B isn't always supported with SAN Storage, but it is almost always supported with host-based replication.

Finally, all your data may not be on the SAN yet, if ever. There may be several important servers that for one reason or another never land on the SAN. Yet you want something more than a backup of these systems and host-based replication could be ideal.

Next, appliance-based replication.

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George Crump is founder of Storage Switzerland, an analyst firm focused on the virtualization and storage marketplaces. It provides strategic consulting and analysis to storage users, suppliers, and integrators. An industry veteran of more than 25 years, Crump has held engineering and sales positions at various IT industry manufacturers and integrators. Prior to Storage Switzerland, he was CTO at one of the nation's largest integrators.