> Is the matric (smallest xor distance) a constant?

I'm confused the metric is a function `fn(PeerID, multihash)`

> As in, if I fetch a block, will it compare my peer ID with the multihash and then if it is below a threshold it'll keep it, otherwise it'll just discard it?

The DHT is used as a mechanism for finding **who** has blocks and telling people that **you** have blocks, not for find/storing the data itself. You may add a block and then you will find the peers in the network that have the smallest metric (colloquially the "closest peers") and tell them the you have the block and other people may come ask you for it.