diff --git a/Rakefile b/Rakefile
index 359ebad..1ec8292 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,5 +1,3 @@
-require 'rake_utils/debian'
-include RakeUtils::DSL
 
 DEBUG  = ENV.has_key?('DEBUG') &&
   %w|yes y ok 1 true t|.include?(ENV['DEBUG'])
@@ -85,8 +83,10 @@ task :clean do
   sh "rm -rf *~ build"
 end
 
-namespace :pkg do
-  deb do |t|
+namespace :pkg do  
+  task :deb do |t|
+    require 'rake_utils/debian'
+    
     t.code_files = ALL_SOURCES + ["Rakefile"]
     t.pkg_name = "flexnbd"
     t.generate_changelog!
diff --git a/src/serve.c b/src/serve.c
index 4c6dd64..f2bc2dd 100644
--- a/src/serve.c
+++ b/src/serve.c
@@ -283,6 +283,21 @@ void client_reply_to_write( struct client_params* client, struct nbd_request req
 				request.len );
 		dirty(client->serve, request.from, request.len);
 	}
+	
+	if (1) /* not sure whether this is necessary... */
+	{
+		/* multiple of 4K page size */
+		uint64_t from_rounded = request.from & (!0xfff);
+		uint64_t len_rounded = request.len + (request.from - from_rounded);
+		
+		CLIENT_ERROR_ON_FAILURE(
+			msync(
+				client->mapped + from_rounded, 
+				len_rounded, 
+				MS_SYNC),
+			"msync failed %ld %ld", request.from, request.len
+		);
+	}
 	client_write_reply( client, &request, 0);
 }
 
diff --git a/tests/flexnbd.rb b/tests/flexnbd.rb
index 8ffb4b7..3864c60 100644
--- a/tests/flexnbd.rb
+++ b/tests/flexnbd.rb
@@ -16,19 +16,24 @@ class FlexNBD
     @port = port
   end
 
-  def serve(ip, port, file, *acl)
+  def serve(file, *acl)
     File.unlink(ctrl) if File.exists?(ctrl)
+    cmd ="#{@bin} serve "\
+         "--addr #{ip} "\
+         "--port #{port} "\
+         "--file #{file} "\
+         "--sock #{ctrl} "\
+         "#{@debug} "\
+         "#{acl.join(' ')}"
     @pid = fork do
-      cmd ="#{@bin} serve "\
-           "--addr #{ip} "\
-           "--port #{port} "\
-           "--file #{file} "\
-           "--sock #{ctrl} "\
-           "#{@debug} "\
-           "#{acl.join(' ')}"
       exec(cmd)
     end
-    sleep 0.1 until File.socket?(ctrl)
+    while !File.socket?(ctrl)
+      pid, status = Process.wait2(@pid, Process::WNOHANG)
+      raise "server did not start (#{cmd})" if pid
+      sleep 0.1
+    end
+    at_exit { kill }
   end
 
   def kill
diff --git a/tests/fuzz b/tests/fuzz
new file mode 100644
index 0000000..e3e3558
--- /dev/null
+++ b/tests/fuzz
@@ -0,0 +1,80 @@
+#!/usr/bin/ruby
+
+require 'flexnbd'
+
+binary      = ARGV.shift
+test_size   = ARGV.shift.to_i
+repetitions = ARGV.shift.to_i
+repetitions = 50 if repetitions == 0
+seed        = ARGV.shift.to_i
+
+max_length  = test_size > 10000000 ? 10000000 : test_size
+CHEAT_AND_ROUND_DOWN = false # set to 'false' to expose bugs
+
+srand(seed)
+
+if test_size < 32768 || repetitions < 1 || !File.executable?(binary)
+  STDERR.print "Syntax: #{$0} <flexnbd bin> <test size> [repetitions] [seed]\n"
+  STDERR.print "test_size must be >= 32768 and repeitions must be >= 1"
+  exit 1
+end
+
+testname_local = "#{$0}.test.#{$$}.local"
+testname_serve = "#{$0}.test.#{$$}.serve"
+[testname_local, testname_serve].each do |name|
+  File.open(name, "w+") { |fh| fh.seek(test_size-1, IO::SEEK_SET); fh.write("0") }
+end
+
+@local = File.open(testname_local, "r+")
+
+@serve = FlexNBD.new(binary, "127.0.0.1", 41234)
+@serve.serve(testname_serve)
+
+repetitions.times do |n|
+
+  begin
+  
+    if File.size(testname_local) != File.size(testname_serve)
+      STDERR.print "Before pass #{n}: File sizes are different: local=#{File.size(testname_local)} serve=#{File.size(testname_serve)}\n"
+      exit 1;
+    end
+
+    md5_local = `md5sum < #{testname_local}`.split(" ").first
+    md5_serve = `md5sum < #{testname_serve}`.split(" ").first
+  
+    if md5_local != md5_serve
+      STDERR.print "Before pass #{n}: MD5 error: local=#{md5_local} serve=#{md5_serve}\n"
+      STDERR.print "**** Local contents:\n"
+      system("hexdump #{testname_local}")
+      STDERR.print "**** Serve contents:\n"
+      system("hexdump #{testname_serve}")
+      exit 1
+    end
+
+    length = rand(max_length)
+    length &= 0xfffff000 if CHEAT_AND_ROUND_DOWN
+    offset = rand(test_size - length)
+    offset &= 0xfffff000 if CHEAT_AND_ROUND_DOWN
+    content = (n%2 == 1) ? ("x" * length) : ("\0" * length)
+  
+    @local.seek(offset, IO::SEEK_SET)
+    @local.write(content)
+  
+    @serve.write(offset, content)
+  
+    if @serve.read(offset, length) != content
+      STDERR.print "After pass #{n}: Didn't read back what we wrote!"
+      exit 1
+    end
+    
+  rescue StandardError => ex
+    STDERR.print "During pass #{n}: Exception: #{ex}"
+    STDERR.print ex.backtrace.join("\n") + "\n"
+    exit 2
+  end
+  
+end
+
+File.unlink(testname_local)
+File.unlink(testname_serve)
+
diff --git a/tests/nbd_scenarios b/tests/nbd_scenarios
index 7392112..be58cfe 100644
--- a/tests/nbd_scenarios
+++ b/tests/nbd_scenarios
@@ -17,7 +17,6 @@ class NBDScenarios < Test::Unit::TestCase
   end
 
   def teardown
-    @nbd1.kill rescue nil
     [@filename1, @filename2].each do |f|
       File.unlink(f) if File.exists?(f)
     end
@@ -73,7 +72,7 @@ class NBDScenarios < Test::Unit::TestCase
 
   protected
   def serve1(*acl)
-    @nbd1.serve(@ip, @port1, @filename1, *acl)
+    @nbd1.serve(@filename1, *acl)
   end
 
   def writefile1(data)