mars/contrib/background-migration-scripts

This CONTRIB directory contains some unsupported _example_ bash scripts
for MARS background data migration.

Method:

0) start point: all resources have two replicas, each on a pair of
nodes. "marsadm view all" shows this as [2/2], meaning two replicas
out of two potential replication hosts.

1) use "marsadm join-cluster" for merging two ordinary replication pairs
into a 4-fold (quadruple) MARS cluster. Now we have [2/4].

2) create two additional resource replicas via "marsadm join-resource".
The new replicas are created in background while the data is being updated
during ordinary production.
Finally we have [4/4] replicas.

3) handover the primary to one node of the _new_ pair.

4) use "marsadm leave-resource" to get rid of the _old_ two replicas.
New replica status is again [2/4], but the the replicas have been
migrated to the new pair in the meantime.

5) Finally, use "marsadm split-cluster" to go back to [2/2].

HINT:

The shell script code is split into two parts: a generic part which
should be usable at more MARS sites in the world, and a 1&1 specific
part which will only work in the 1&1 Shared Hosting Linux environment.

However, by looking at the code, you should be able to create your own
adaptations.