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Your data protection plan must consider latency in WAN-based replication

It's a common sense solution to data protection -- keep a spare copy of your data in an off-site location. But keeping that data synchronized -- and secure -- is an important consideration as well. In this Storage Decisions video, Jon Toigo, CEO of Toigo Partners International, highlights some issues that IT pros need to address as part of their data protection plan.

"Basically, if the building fails, you're going to need another building to recover in somewhere else. We all remember that there were issues as to how far away that secondary facility, that secondary instantiation of disk or tape or whatever, should be," Toigo said.

"We have to put our recovery area somewhere far away. The problem is we run into the issues of latency -- a signal doesn't fly as the crow flies, and frankly, the farther a signal has to go, the more delay accrues to it," said Toigo, who later added, "We also have what is known as 'jitter' in shared WANs. … Inside that cloud that you're moving your data through are a whole bunch of routers. And open-shortest-path-first doesn't mean, 'Give me the shortest distance between A and B; it means, 'Give me the shortest number of router hops.'"

Toigo noted that off-site backup can create the issue of data deltas, where you have differences in the state of data in two locations.

"That can be a real big issue when trying to recover back to a certain point in time or satisfy a service-level agreement that says I will only lose x number of transactions in the solution I've provided," Toigo said.

"Does that mean WAN-based replication is no good? No, of course it doesn't," Toigo said. "Use it judiciously, do a lot of testing and make copies of your data to tape in any case. Because if you lose that WAN link while replication is going on, chances are very good that you'd lose everything in the pipeline, as well as the data you just lost from the hard disks themselves."

Toigo said backing up to a cloud is also impacted by that whole latency issue and that isn't a fix for everything that ails your backup.

"Please, be sensible about it and test it, and remember clouds themselves have to protect your data. Are you sure they are doing that as well as you would? … If you're a hospital or health care institution, you don't transfer responsibility to the folks doing DR backup in a cloud. … You've extended responsibility out to them, but you're still primarily responsible for the safekeeping of that data," Toigo said.

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