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Three data replication choices have emerged: array-based, host-based and network-based, with each having its distinct pros and cons. What method is best for your environment?
When it comes to preparing for an eventual disaster, it's better to scatter your eggs rather than fortify your basket. That risk-mitigation philosophy is at the heart of an important storage trend: replicating data to remote locations. And, increasingly, it's not enough for those copies to be offline on tape. Replicated data needs to be readily accessible—online—so that operations can resume as quickly as possible in the event of an outage at the primary site.
"We still do tape backup at night, but we wouldn't want to lose an entire day's worth of data," says Don Moran, database administrator at Hanson Brick & Tile, a brick manufacturer headquartered in Charlotte, NC. The company began replicating the Oracle database that runs its enterprise resource planning system in North Carolina to a Hanson office in Texas approximately two years ago. Disaster recovery (DR) tests have shown Moran that he can get his standby server up and running in less than 15 minutes. "I can go into full DR mode without ever leaving my office," he says.
Storage readers are very keen on replication. According to a survey published in our March issue (see "Snapshot"), the portion of readers doing remote replication has shot up almost 20 percentage points, from 38% to 57%, in the past 18 months. This surge of interest goes hand-in-hand with the growing number of replication products that are on the market. Ten years ago, there were only a handful of replication products, and none of them was cheap. Replication was limited to the domain of those financial firms with the deepest pockets, and the target sites weren't very distant. These days, even small- to medium-sized businesses are replicating select data sets, sometimes thousands of miles away (see "Evaluate your environment").
But even though the economics of replication have changed dramatically, the technology changes have been relatively incremental. In the beginning, replication took place on the host. Large storage vendors eventually began offering replication as a function of their arrays. Today, startups are angling to have more replication take place off the host or array and in the network instead; each approach has its pros and cons.
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