HDFS across data centers: HighTide

There are many instances when the same piece of data resides on multiple HDFS clusters in different data centers. The primary reason being that the physical limitation of one data center is insufficient to host the entire data set. In that case, the administrator(s) typically partition that data into two (or more) HDFS clusters on two different data centers and then duplicates some subset of that data into both the HDFS clusters.

In such a situation, there will be six physical copies of data that is duplicated, three copies in one data center and another three copies in another data center. It would be nice if we can keep fewer than 3 replicas on each of the data centers and have the ability to fix a replica in the local data center by copying data from the remote copy in the remote data center.