user105526: 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.

user63872: 
If yes then how the data is decentralised. It is just a large network of centralised database.

When people use the term decentralized, they mean that there is no central point of authority; no heirarchy to the network's nodes. 
Each bitcoin full node validates the full network state, which allows them to participate in the network without having to trust any specific peer to provide them with truthful information. This is an important property of the network. 
What you seem to be implying is that the blockchain history data itself should be stored/communicated in a decentralized way. But if each node was not able to fully verify the entirety of the data itself, then it would have to trust that other nodes in the network have verified the info it is missing. This is an issue, since now every node will have to trust third party nodes to provide truthful updates. Under this model, we lose the very important aspect of trustless participation, and instead end up with a Byzantine mess. 

user101498: 
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.

105526: <p>Since the copy of same data is storedon each node in network. Does it use storage space to store same data on each node? </p>

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

<p>Any help would be appreciated.</p>
 63872: <blockquote>
  <p>If yes then how the data is decentralised. It is just a large network of centralised database.</p>
</blockquote>

<p>When people use the term <em>decentralized</em>, they mean that there is no central point of authority; no heirarchy to the network's nodes. </p>

<p>Each bitcoin full node validates the full network state, which allows them to participate in the network without having to trust any specific peer to provide them with truthful information. This is an important property of the network. </p>

<p>What you seem to be implying is that the blockchain history data itself should be stored/communicated in a decentralized way. But if each node was not able to fully verify the entirety of the data itself, then it would have to trust that other nodes in the network have verified the info it is missing. This is an issue, since now every node will have to trust third party nodes to provide truthful updates. Under this model, we lose the very important aspect of trustless participation, and instead end up with a Byzantine mess. </p>
 101498: <blockquote>
<p>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?</p>
</blockquote>
<p>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.</p>
<blockquote>
<p>If yes then how the data is decentralised. It is just a large network of centralised database.</p>
</blockquote>
<p>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.</p>
