Reading and Writing of data is done via the file system cache. SAS does not use direct IO by default. NOTE: Since SAS uses the file system cache to read and write data, the maximum IO throughput rate is restricted by how fast the file system cache can process the data. The maximum file system cache throughput we have seen in testing has been a little over 2GB/sec on modern UNIX and LINUX servers, with a peak at around 1.4 GB/second on 64-bit Windows Servers. Your experience may vary as these tests were on maximized, highly provisioned systems.