Q

Looking at two-way replication methods

We are planning to extend our project to other locations (overseas). One of the objectives is to replicate the database two-way. What tool would you recommend?

By two-way replication, I assume you mean that you have some data at your domestic location and some other, unrelated data at your overseas location, and you wish you replicate each site's data to the other site.

If your intent is to modify the same data in both locations at the same time, that won't work as the latency introduces windows of vulnerability where two people can modify the same record at the same time creating conflicts.

So, assuming the first situation is your goal, to replicate over the kind of distance you are talking about, asynchronous replication is pretty much a requirement. The latency (delay) that synchronous replication can introduce is sure to be quite significant, probably slowing your application to an unacceptable crawl.

(Full disclosure time: I work for Veritas Software.)

In my experience, hardware replication solutions such as EMC's SRDF and Hitachi's True Copy do not handle asynchronous replication as well as software-based replication solutions like Veritas' Volume Replicator or Sun's StorEdge Availability Suite's remote mirror software.

I would recommend however, that you price out both a hardware and a software solution and then run some performance benchmarks over the distance you wish to replicate and see which solution gives you better price/performance. Make sure that the data that you replicate emulates as closely as possible the data you'll have in production, in terms of quantity (number of blocks), size of the blocks, burstiness, rate, number of parallel users, line speed, and like that.

Good luck!

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This was first published in January 2003

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