Just a little idea to help out with reducing fragmentation on the filesystem and reducing seek-overheads. If you have full prealloc enabled in the client and you start to download a few torrents (at almost the same time) these will be preallocated at the same time and this causes a big jump in seek-times on the drives and also (depending on how many torrents it is) almost a hang of ktorrent. It would be nice to see if you could limit preallocs to 1 at a time or a user-specified value.

Just a thought.

Not a bad idea

Related: for some time there's been this fallocate call available, which calls filesystem specific allocation for XFS and ext4 and regular posix_fallocate for others.