When to use host-based replication

What you will learn from this tip: How, when and why to use host-based replication instead of the pricier, centralized, storage-based variety.

Host-based replication is often used in smaller environments or on a departmental basis. A host-based solution can be deployed at a fraction of the cost of a high-end, storage-based implementation, even considering the cost of software licenses, hardware and implementation services.

Host-based replication typically resides at the file system or logical volume level within the operating system. Like storage-based offerings, it's usually transparent to the application, but certainly not transparent to the host operating system or hardware. In most cases, asynchronous replication over the LAN or WAN to a similar (not necessarily identical) system is provided. Distance isn't usually an issue and heterogeneous storage can be deployed easily in a given configuration. Also, most products can transfer data at the byte level rather than the data block level, potentially requiring less bandwidth.

So, what's the downside? One issue is that it's a decentralized solution in a time when most of IT is trending toward centralization. We're consolidating data centers, servers and storage, so why would we decentralize an important disaster recovery (DR) function like replication? However, costs often outweigh thi

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More practical concerns are scalability and performance. Host-based solutions, by definition, have some degree of impact on the CPU and other server resources. A good understanding of data change rates, resource utilization patterns and available capacity is important when determining if this type of solution will meet your needs.

Manageability and support must also be considered. It's easy to deploy host-based replication on a few servers, but if widely deployed it can complicate server management.

Where does it fit?

When is host-based replication an option? If synchronous replication is required, most host-based solutions are ruled out. Similarly, host-based solutions don't support the notion of consistency groups. But there are many cases where a host-based option may fit, including: The replication landscape is evolving. Functionality once found only on high-end arrays is now offered on midtier Fibre Channel and iSCSI platforms. And advances in network-based solutions may change the economics of replication.

In any event, we should strive to find the appropriate tool for the job. For many, host-based replication is the right tool at the right price.

Read the full tip in Storage magazine.

For more information:

Tip: Replication for high availability

Topics: Replication

Tip: The evolving role of data replication

About the authors: James Damoulakis is CTO and Phil Poresky is storage practice manager for GlassHouse Technologies.

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