MapReduce is the Google idea from before 2004 how to do calculations on lot's of data. Now there is also YARN that could be described as a general job scheduler.
At the moment a lot of people use software on YARK like Spark (does more in memory, is faster, can use the GPU on the cluster machines).
So if you have biological data you could feed that into a HDFS and have Spark or MapReduce jobs that process the data. The clue about Hadoop is that don't need to care about getting the clustering and distributed setup right. This is done by Hadoop for you. You program like you would program a single thread algorithm (at least in the simple cases).
E.g. this Python code counts words over as much data as you want in parallel: http://www.michael-noll.com/tutorials/writing-an-hadoop-mapr...
If you google each of these projects you'll find a lot of information.
Here are the original papers that should give a good idea:
- HFDS (Google Filesystem was the original idea - Hadoop was a free implementation by Yahoo - http://static.googleusercontent.com/media/research.google.co...
- MapReduce - http://static.googleusercontent.com/media/research.google.co...
- Spark: http://www.cs.berkeley.edu/~matei/papers/2010/hotcloud_spark...
If you want a good introduction read Hadoop: The Definitive Guide, 3rd Edition
We used it for building a search engine out of multiple terabytes of crawl data - something that fit's not good on a single computer.
You can do all kinds of computations but graph problems or things that not good to parallelize require often other solutions beyond MapReduce or more thought - MapReduce also only fits for a certain class of problems - it's great for counting and aggregation of stuff but beyond that it's often not usable.
The problem is pulling that off. Sure if you are clever and pursue a PhD it's worth going the abstract theoretical route but in my personal experience as a somewhat stupid student it's fine to look for a niche and get hands-on experience on that.
Mastering Hadoop is still far from easy and if you need to use it without burning tons of CPU cycles it's even harder to get right.