How long does it take to process the file If I have only one worker node?

Let's say I have a data with 25 blocks and the replication factor is 1. The mapper requires about 5 mins to read and process a single block of the data. Then how can I calculate the time for one worker node? The what about 15 nodes? Will the time be changed if we change the replication factor to 3? I really need a help.

First of all I would advice reading some scientific papers regarding the issue (Google Scholar is a good starting point).

Now a bit of discussion. From my latest experiments I have concluded that processing time has very strong relation with amount of data you want to process (makes sense). On our cluster, on average it takes around 7-8 seconds for Mapper to read a block of 128MBytes. Now there are several factors which you need to consider in order to predict the overall execution time:

1. How much data the Mapper produces, which will determine moreless the time Hadoop requires to execute Shuffling
2. What Reducer is doing? Does it do some iterative processing? (might be slow!)
3. What is the configuration of the resources? (how many Mappers and Reducers are allowed to run on the same machine)
4. Finally are there other jobs running simultaneously? (this might be slowing down the jobs significantly, since your Reducer slots can be occupied waiting for data instead of doing useful things).

So already for one machine you are seeing the complexity of the task of predicting the time of job execution. Basically during my study I was able to conclude that in average one machine is capable of processing from 20-50 MBytes/second (the rate is calculated according to the following formula: total input size/total job running time). The processing rate includes the staging time (when your application is starting and uploading required files to the cluster for example). The processing rate is different for different use cases and greatly influenced by the input size and more importantly the amount of data produced by Mappers (once again this values are for our infrastructure and on different machine configuration you will be seeing completely different execution times).

When you start scaling your experiments, you would see in average improved performance, but once again from my study I could conclude that it is not linear and you would need to fit by yourself, for your own infrastructure the model with respective variables which would approximate the job execution time.

Just to give you an idea, I will share some part of the results. The rate when executing determine use case on 1 node was ~46MBytes/second, for 2 nodes it was ~73MBytes/second and for 3 nodes it was ~85MBytes/second (in my case the replication factor was equal to the number of nodes).

The problem is complex requires time, patience and some analytical skills to solve it. Have fun!