This example describe how to define passive partitions and how to use 
multi data storage feature.

sp1 is configured on part1. We use dfs://storage1 as a data storage
support for part1. part1 is an active partition.

sp2 is configured on part2. We use dfs://storage2 as a data storage
support for part2. part2 is an active partition.

sp3 is configured on part3. We use dfs://storage3 as a data storage
support for part3. part3 is a passive partition.

Create four directories storage1, storage2, storage3 and storage4.

Run in two separate sessions:

part1

and

part2 --data_location dfs://storage4


Look at the files created in storage1, storage2, storage3 and storage4.

part1 has updated all the variables sp[123].x_p1.
part2 has updated all the variables sp[123].x_p2.

Note that variables from sp1 are stored in storage1, variables from sp3
are stored in storage3. variables from sp2 are stored in storage4 because
of the command line argument passed to part2.

