On Wed, 2008-04-02 at 12:29 +0800, Ed Greshko wrote: > Patrick O'Callaghan wrote: > > > Just installed Azureus and tested it. It behaves exactly the same as > > Ktorrent, both with and without preallocation. > > > > This is hardly surprising as we're talking about how the filesystem > > works, not about about a specific application. As someone else pointed > > out, a inconsistency between the results of 'du' and 'df' can occur when > > a running process has an open file which has been unlinked, meaning the > > space occupied by the file has not yet been reclaimed even though the > > file no longer has a name. However, any inconsistency arising from this > > would be in the *opposite* direction to what the OP is seeing, i.e. less > > actual free space than accounted for by the filesystem size less the > > space occupied by (visible) files. > > > > In all of this I've been assuming that preallocation means what it has > > always meant traditionally in Unix/Linux: write garbage into the file to > > make sure disk space is allocated. It turns out the system can now do > > this for you, with the fallocate() call. However this is a very recent > > addition and people were still arguing about its semantics less than a > > year ago -- see http://lwn.net/Articles/240571. One detail stands out: > > with the correct parameter, the apparent size of the file (as reported > > by the stat() call) does not change, even if space is allocated beyond > > its end. The effect of this on 'df' and 'du' doesn't seem to be > > documented anywhere. Furthermore, although it's not explicitly stated, > > one presumes that the unused space is reclaimed when the file is closed, > > so the OP's question still stands: how can 'du' report more space than > > is being used, even if no processes have open files? For that matter, > > how can the system preallocate more space than the size of the > > filesystem? Doesn't make sense. > > > > BTW, it might be worth knowing what filesystem the OP is using. In my > > case it's ext3. > > FWIW, the OP is probably happy to have his problem solved. Chances are he > is running ext3 as most people take the default. > > What would be more interesting would be to know what file system you are > running. ext3, as I already said. poc
