Torrents and Files

Searching for Existing Files

Common Questions

Why are files being created/allocated on disk when they are deselected?

A multi-file torrent lists the files contains within it in order (commonly alphabetically but it doesn't have to be).

Let's call these files A, B, C and D.

The BitTorrent protocol deals with things called 'pieces' of a fixed size (apart from the last piece which may be smaller) - this size is selected by the torrent creator but is a power of 2 - for example 16KB, 256KB, 4MB.

The files (A,B,C,D in this example) are logically laid out in order and the pieces allocated sequentially. If we have a piece size of 16KB then the first 16KB of file A will be piece 1, the next 16KB piece 2 etc until the end of file A is reached. At this point whatever bytes are needed from file B to complete the piece are used. Say file A was 41KB in size. The first 2 pieces would use the first 32KB of A. This would leave 9KB remaining so piece 3 would be made up from the last 9KB from file and the first 7KB from file B (assuming B was at least 7KB in size - if it was less then all of B would be used and some of C...)

So you can see that pieces at the end of the file will in general be made up from parts of from multiple files.

In order to download a file the BitTorrent protocol demands that all of the pieces that it contains be downloaded and stored on disk (they must be stored as in order to seed data to other peers entire pieces are needed, it is not possible to seed a partial piece).

So in the example above in order to download file A it is necessary to also download the first 7KB of file B.

Even if you have deselected file B and have no interest in it whatsoever it will be necessary to download the start of file B.

This is why you will see deselected files being created when downloading.

You might say 'why can't BiglyBT store these files somewhere else hidden away to stop burning my eyes with unwanted files?' Well, it could, but it doesn't. The main reason is that if you wanted to reseed the torrent at a later time you would need the partial file contents to be able to do so. If they were hidden away you wouldn't be able to do this.

You can however configure BiglyBT to rename such files with an extension, or put them into a subdirectory. See Options->Files.