Storage Replication Breaks Ties

Data replication is shape-shifting as it grows in importance to storage managers, and emerging trends signal simpler and cheaper approaches.

The expanded role of replication is no surprise, since there's simply more data out there that needs protection. At the same time, users are taking a longer look at timeworn replication methods in search of something better.

To see what's new requires a look at the status quo. In general, replication is still tied to backup, with one copy made locally and a second copy sent offsite. And it's typically done in storage arrays or alternatively in software at the server.

Both approaches have pros and cons. On the array side, replication tools that come with SANs from EMC, HP, IBM, and others have distinct pros and cons.

Let's start with the pros: "[SAN array-based replication] provides an effective single point of data replication for mission critical data," points out George Crump of the Storage Switzerland consultancy. Array-based replication is usually more scalable, he says. It can be cheaper than software replication for large installations in which software-based wares would call for multiple licenses. And it can support any operating systems that attach to the SAN, "for example, that OpenVMS box that you may still have," Crump asserts.On the other hand, SAN vendors may resist replicating to other vendors' wares. And not all kinds of businesses can afford expensive SANs.

Software products from vendors such as CA XOsoft, Double-Take, and Symantec aren't tied to specific vendor's hardware. If you're looking to save on SAN gear, these products can help you do it. On the other hand, they may not be as scalable as array-based solutions.

While it's erroneous to draw hard and fast lines across products, since many overlap, users are finding it useful to describe a third group of replicators, loosely dubbed "network-based replication tools."

Usually sold as appliances or on dedicated servers, these wares combine the strengths of both array- and software-based solutions, experts say. Most incorporate CDP as well as replication, and most have added VMware support.

Vendors in this space include InMage with its DR-Scout; EMC, via its acquisition of Kashya; and FalconStor, via its newly announced CDP Virtual Appliance for VMware, to name a few."The advantage of replication in the network versus at the edge via host- or storage-based systems, is that you can have heterogeneous hosts and heterogeneous storage, including multiple distinct products from the same vendor," says one industry analyst, who asked not to be named.

"All three methods will prevail, but in general I see the network-based replication products will dominate over time," says Arun Taneja of the Taneja Group. In his view, there will always be a need for high-end array-based replication tools like EMC's SRDF, used with Symmetrix systems. Low-end to midrange customers will do well with host-based products. But for companies looking to replicate across different arrays or hosts, network-based replication will become increasingly attractive, Taneja thinks.

Another trend in replication is virtualization. Support for VMware is now a given across replication tools, with features and functions on the uptick. Double-Take, for instance, now offers byte-level replication not just from one server to another or between VMs on one ESX server but between VMs on geographically distinct ESX servers.

End users are just starting to unravel the issues and iterations of today's replication wares. "I've looked at some of the appliance-based solutions," says Steven Olson, technical services manager at the Las Vegas Review-Journal. "I like the flexibility they are offering, providing any-to-any solutions. These seem to be the immediate future of storage replication."

But Olson thinks much more shape-shifting is in store. "In the end, I think total virtualization of storage will become far more prevalent, adding a layer of high intelligence between the hosts and all storage."Have a comment on this story? Please click "Discuss" below. If you'd like to contact Byte and Switch's editors directly, send us a message.