diff --git a/s3tests/realistic.py b/s3tests/realistic.py
index 5e063e8..f86ba4c 100644
--- a/s3tests/realistic.py
+++ b/s3tests/realistic.py
@@ -21,6 +21,7 @@ def generate_file_contents(size):
     should remove the last 40 chars from the blob to retrieve the original hash
     and binary so that validity can be proved.
     """
+    size = int(size)
     contents = os.urandom(size)
     content_hash = hashlib.sha1(contents).hexdigest()
     return contents + content_hash
@@ -28,22 +29,29 @@ def generate_file_contents(size):
 
 class FileValidator(object):
 
-    def __init__(self, f):
+    def __init__(self, f=None):
         self._file = tempfile.SpooledTemporaryFile()
-        f.seek(0)
-        shutil.copyfileobj(f, self._file)
-        self.seek(0)
+        self.original_hash = None
+        self.new_hash = None
+        if f:
+            f.seek(0)
+            shutil.copyfileobj(f, self._file)
 
     def valid(self):
         """
         Returns True if this file looks valid. The file is valid if the end
         of the file has the md5 digest for the first part of the file.
         """
-        contents = self._file.read()
         self._file.seek(0)
-        original_hash, binary = contents[-40:], contents[:-40]
-        new_hash = hashlib.sha1(binary).hexdigest()
-        return new_hash == original_hash
+        contents = self._file.read()
+        self.original_hash, binary = contents[-40:], contents[:-40]
+        self.new_hash = hashlib.sha1(binary).hexdigest()
+        if not self.new_hash == self.original_hash:
+            print 'original  hash: ', self.original_hash
+            print 'new hash: ', self.new_hash
+            print 'size: ', self._file.tell()
+            return False
+        return True
 
     # XXX not sure if we need all of these
     def seek(self, offset, whence=os.SEEK_SET):
@@ -55,6 +63,10 @@ class FileValidator(object):
     def read(self, size=-1):
         return self._file.read(size)
 
+    def write(self, data):
+        self._file.write(data)
+        self._file.seek(0)
+
 
 class RandomContentFile(object):
     def __init__(self, size, seed):
@@ -228,6 +240,7 @@ def files(mean, stddev, seed=None):
                 break
         yield RandomContentFile(size=size, seed=rand.getrandbits(32))
 
+
 def files2(mean, stddev, seed=None, numfiles=10):
     """
     Yields file objects with effectively random contents, where the
@@ -238,17 +251,17 @@ def files2(mean, stddev, seed=None, numfiles=10):
     stores `numfiles` files and yields them in a loop.
     """
     # pre-compute all the files (and save with TemporaryFiles)
-    rand_files = files(mean, stddev, seed)
     fs = []
     for _ in xrange(numfiles):
-        f = next(rand_files)
         t = tempfile.SpooledTemporaryFile()
-        shutil.copyfileobj(f, t)
+        t.write(generate_file_contents(random.normalvariate(mean, stddev)))
+        t.seek(0)
         fs.append(t)
 
     while True:
         for f in fs:
-            yield PrecomputedContentFile(f)
+            yield f
+
 
 def names(mean, stddev, charset=None, seed=None):
     """