The especially odd thing about the background deletion is that it does an ltrunc on each file, shortening it by 20MB at a time until it has zero length. I just can't see how this can possibly be any more efficient or light on CPU than just removing the file's index entry with unlink. This has the smells of someone looking for a problem to apply a clever solution to. Now, if they'd commented it with workaround for unlink being slow across networks/due to a bug in drivers on Miraclebox 123 then we'd know where we were.