Practices, scripts (R and Python), data and challenges for different problems of machine learning can be found at hackerearth. Within the challenges one can find a lot of datasets which could be used for your regard - depending on what you mean with BIG data. Have a look at:

https://www.hackerearth.com/practice/machine-learning/machine-learning-algorithms/

R-Programming, RapidMiner, Knime , NodeXL

See please this link

https://bigdata-madesimple.com/70-websites-to-get-large-data-repositories-for-free/

and this also

https://bigdata-madesimple.com/70-websites-to-get-large-data-repositories-for-free/

Dear Kiran Adnan ,

Please check below mentioned links for unstructured datasets repo:-

Natural Earth Data : http://www.naturalearthdata.com/downloads/

Geocomm : http://data.geocomm.com/drg/index.html

Geonames data: http://www.geonames.org/

Best regards!

Gourav Gupta

social media data are mostly unstructured data u can have freely.