When you begin to upload a file to Sia, it has to get processed on your machine to allow for maximum redundancy and security on the network. It is first split into manageable chunks. Each chunk is then run through a process that creates 30 pieces, each of which gets encrypted before being sent to a different host. Only 10 of the 30 pieces are needed to reconstruct a chunk, but no host ever sees more than one. This means, for each part of your original file, 20 hosts could drop from the network and your data will still be safe and secure.