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With Tungsten Replicator Continuent is trying to deliver a better master/slave replication system. Their goal: scalability, reliability with seamless failover, no performance loss.

From their website:
The Tungsten Replicator implements open source database-neutral master/slave replication. Master/slave replication is a highly flexible technology that can solve a wide variety of problems including the following:

* Availability - Failing over to a slave database if your master database dies
* Performance Scaling - Spreading reads across many copies of data
* Cross-Site Clustering - Maintaining active database replicas across WANs
* Change Data Capture - Extracting changes to load data warehouses or update other systems
* Zero Downtime Upgrade - Performing upgrades on a slave server which then becomes the master

The Tungsten Replicator architecture is flexible and designed to support addition of new databases easily. It includes pluggable extractor and applier modules to help transfer data from master to slave.

If you are trying to create highly available file systems, especially across data centers, then ChironFS is one potential solution. It's relatively new, so there aren't lots of experience reports, but it looks worth considering. What is ChironFS and how does it work?

File replication based on erasure codes can reduce total replicas size 2 times and more.