Data storage within hyperledger

Question

I have started learning hyperledger. Became familiarised with it by creating a sample app using the composer playground. My doubt is regarding the decentralized storage using hyperledger. I have read some few docs which mentions about :

• Saving the hash of the data within the blockchain to ensure the immutability.

• Saving the image within the blockchain(as an asset) through the base64 string.

Some of the things were clear but a large portion still remains uncertain. They are :

• Where is the data stored within the blockchain? Is it in couchdb ?
• Suppose the data is stored within the couchdb and via multipeer a new peer gets added to the channel, then does it mean that all the couchdb's of the peers get synced ?

Any resources/tutorials that mention about data storage with the blockchain, decentralized storage etc. would be very helpful.

Thanks!

Answer 1

the blockchain data, aka the ledger, is stored as a physical file. it contains linked blocks, each block consisting of a set of transactions. Each state change is stored there.

By contrast, the world state only contains the current state of every asset as that's what applications need.

The world state is implemented as a database, couchdb being a good option, there is a simpler one available but that one offers much less in terms of querying capability.

Of course what this means is that the world state can be easily recreated from the ledger at any point in time.

when a new peer gets added to a channel, its own world state is created from the ledger.

a good read describing all this is here: https://hyperledger-fabric.readthedocs.io/en/release-1.3/ledger/ledger.html