Allow mounting 2 separate persistent volumes for dataDir and dataLogDir

[rodolphogarrido]

Description

Proposal for allowing mounting 2 separate persistent volumes for dataDir and dataLogDir.

Importance

As mentioned in Zookeeper oficial doc:

Be careful where you put the transaction log. A dedicated transaction log device is key to consistent good performance. Putting the log on a busy device will adversely affect performance

Having a dedicated log device has a large impact on throughput and stable latencies. It is highly recommended to dedicate a log device and set dataLogDir to point to a directory on that device, and then make sure to point dataDir to a directory not residing on that device.

We could benefits in latency by separating these two directories.

Suggestions for an improvement

Allow mounting 2 separate persistent volumes for dataDir and dataLogDir.