Why does my hard drive go crazy at the beginning of a resumed download?
First, you may want to review the answers to the question on terminology. A seed is a client which has a complete file. Seeding is the process of connecting to a torrent when you have a complete file. There are two ways to do this: • …by leaving your client open after the download completes. Once you have the entire file you become a seed, and the BitTorrent client remains connected to the swarm, sending to other users until you close it. • …by clicking on a torrent link (or opening a saved .torrent file) and selecting a filename of a file that has already completed. BitTorrent will check over the file and realize that it’s already complete, and continue to connect to the tracker and serve as a seed. It’s generally considered a good idea to leave your client open as long as possible, since it helps other users.
When you open a torrent and give BitTorrent a filename/directory that already exists, it must check the file to see how much of it is useful data and how much is junk. (Recall that BT allocates space for the entire file when you first start a torrent.) To do this it must read the entire contents of the file, and generate what’s known as a hash for each piece of the file. A hash is a cryptographic function that creates a small summary or digest of a large amount of data. BitTorrent uses the SHA hash function to determine which parts of the file are good and which are bad.