This is not accurate.
There is no API to know for sure. Put you can have a lower bound by asking for peer having a copy of the data on the DHT.
The original provider of the data will
ipfs add theirData. This means
that it will advertise on the DHT “hey guys, if you want a copy of the data corresponding to this hash, I can sent it to you”. Adding will also automatically
pin the data on this node, meaning this node will never garbage collect it, and will keep it available until it’s unpinned.
Any other node can request the data. The canonical way to do that is to query the DHT, that will give you addresses of peers with content. At first, only the original publisher will have it. Once the querying nodes have the data, they got 2 choices: making it available until it’s garbage collected (meaning while the data is its own cache) or pin it, to keep it on its node.
When a third peer asks for this data, the DHT will give it the addresses of the 2 previous nodes. And so on.
Please take note that you pin data on a node. The same piece of data can be pinned by node A and not by node B.
Any node can decide to pin the content (on itself).
From a publisher’s point of view, once the data has been requested and sent, a copy is out there, and there is no way to control its propagation.
More generally, with any information, on any technology, once someone you have no control over has a copy, you can’t control how this information will be shared.
When a piece of data was published, the CID (~hash) of the content was published, but no one online has a copy of it anymore, either because it’s not pinned and not in cache, or because nodes having it are online.
Content is not replicated automatically. It is if a lot of nodes asks for the content (it is popular) or if they pin it (either because they like it or because you pay them to do so: we call that a pinning service).
Filecoin will be a decentralized pinning service.
Filecoin is in alpha, an alphanet is online and a testnet will be on Dec 11. You can’t use you filecoins (FIL) to rent storage space yet. At this point, it’s still speculation before the main launch
The mainnet is expected Q1 2020.