Bill Bridge created ZOOKEEPER-1508:
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Summary: Reliable standalone mode through redundant databases
Key: ZOOKEEPER-1508
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1508
Project: ZooKeeper
Issue Type: New Feature
Environment: Single server with multiple disks or two node cluster
with multiple shared disks
Reporter: Bill Bridge
Currently ZooKeeper requires 3 servers to provide both reliability and
availability. This is fine for large internet scale clusters, but there are
lots of two node clusters that could benefit from ZooKeeper. There are also
single server use cases where it is highly desirable to have ZooKeeper survive
a disk failure, but availability is not as important.
This feature would allow the configuration of multiple destinations for logs
and snapshots. A transaction is committed when a majority of the log writes
complete successfully. If one log gets an error on write, then it is taken
offline until an administrator brings it online or replaces it with a new
destination. ZooKeeper continues to run as long as a quorum of disks can be
written.
High availability can be provided with a two node cluster. When the ZooKeeper
node dies, the disks are switched to the surviving node and a new ZooKeeper
starts. Faster switch over can be done if there is an observer already running
in the new node.
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