Problem with data redundancy in block chain Since the copy of same data is storedon each node in network. Does it use storage space to store same data on each node? 

If yes then how the data is decentralised. It is just a large network of centralised database.

Any help would be appreciated.
Since the copy of same data is stored on each node in network. Does it use storage space to store same data on each node?

Yes, but what matters is the validation of the data. Therefore you can use pruning to validate the block chain data without the storage overhead.

If yes then how the data is decentralised. It is just a large network of centralised database.

What can be called decentralisation in the case of Bitcoin is the ability of being able to retrieve the current state of the network without having to trust a central source of validation (/truth). This is accomplished through the validation of the block chain.