What NTFS allocation unit size (also called cluster size, or block size) should be used when creating or formatting Logical Unit Number (LUNs) for Microsoft SQL Server and Microsoft Exchange? Sequenti...What NTFS allocation unit size (also called cluster size, or block size) should be used when creating or formatting Logical Unit Number (LUNs) for Microsoft SQL Server and Microsoft Exchange? Sequential Read and Write Test (transfer size = 64KB) - the differences between the allocation unit sizes of 4K and 64K are 4% for sequential reads and less than 1% for sequential writes.