Finally we did it. Problem was raid5. We destroy raid and replaced by raid50. Now reading is 700 mb/s. Writing is arround 280 mb/s. Also if the client macpro has macos 10.5.7 everthing is ok with 700 mb/s reading and 280 mb/s writing. When we update macpro to 10.6.2 (snow leopard) reading is 300 mb/s writing is 300 mb/s without any problem.
Thanks for your help @r3Vo.
Regards..