How to do non-cached file writes in C# winform app

Question

I\'m trying to determine worst case disk speed, so I wrote the following function.

static public decimal MBytesPerSec(string volume)
{
    string filename =         


        

Answer 1

Try some unmanaged code:

[DllImport("kernel32", SetLastError = true)]
        static extern unsafe SafeFileHandle CreateFile(
            string FileName,           // file name
            uint DesiredAccess,        // access mode
            uint ShareMode,            // share mode
            IntPtr SecurityAttributes, // Security Attr
            uint CreationDisposition,  // how to create
            uint FlagsAndAttributes,   // file attributes
            IntPtr hTemplate // template file  
            );
const uint FILE_FLAG_NO_BUFFERING = 0x20000000;

SafeFileHandle handle = CreateFile("filename",
                            (uint)FileAccess.Write,
                            (uint)FileShare.None,
                            IntPtr.Zero,
                            (uint)FileMode.Open,
                             FILE_FLAG_NO_BUFFERING,
                            IntPtr.Zero);

var unBufferedStream = new FileStream(handle,FileAccess.Read,blockSize,false);

now you should have access to an unbuffered stream which you can read and write however you please with no constraints

For the record....you can also disable caching like this:

[DllImport("KERNEL32", SetLastError = true)]
        public extern static int DeviceIoControl(IntPtr hDevice, uint IoControlCode,
            IntPtr lpInBuffer, uint InBufferSize,
            IntPtr lpOutBuffer, uint nOutBufferSize,
            ref uint lpBytesReturned,
            IntPtr lpOverlapped);
        [DllImport("KERNEL32", SetLastError = true)]
        public extern static int CloseHandle(
        IntPtr hObject);

[StructLayout(LayoutKind.Sequential)]
        public struct DISK_CACHE_INFORMATION
        {            
            public byte ParametersSavable;            
            public byte ReadCacheEnabled;            
            public byte WriteCacheEnabled;
            public int ReadRetentionPriority;//DISK_CACHE_RETENTION_PRIORITY = enum = int
            public int WriteRetentionPriority;//DISK_CACHE_RETENTION_PRIORITY = enum = int
            public Int16 DisablePrefetchTransferLength;//WORD            
            public byte PrefetchScalar;            
        }

public void SetDiskCache(byte val)
        {
            IntPtr h = CreateFile("\\\\.\\PHYSICALDRIVE0", (uint)FileAccess.Read | (uint)FileAccess.Write, (uint)FileShare.Write, IntPtr.Zero, (uint)FileMode.Open, 0, IntPtr.Zero);
            DISK_CACHE_INFORMATION sInfo = new DISK_CACHE_INFORMATION();
            IntPtr ptrout = Marshal.AllocHGlobal(Marshal.SizeOf(sInfo));
            Marshal.StructureToPtr(sInfo, ptrout, true);            
            uint dwWritten = 0;
            int ret = DeviceIoControl(h,IOCTL_DISK_GET_CACHE_INFORMATION,IntPtr.Zero,0,ptrout,(uint)Marshal.SizeOf(sInfo),ref dwWritten,IntPtr.Zero);            
            sInfo = (DISK_CACHE_INFORMATION)Marshal.PtrToStructure(ptrout,typeof(DISK_CACHE_INFORMATION));            
            sInfo.ReadCacheEnabled = val;
            // acuma trimite structura modificata
            IntPtr ptrin = Marshal.AllocHGlobal(Marshal.SizeOf(sInfo));
            Marshal.StructureToPtr(sInfo, ptrin, true);            
            ret = DeviceIoControl(h, IOCTL_DISK_SET_CACHE_INFORMATION, ptrin, (uint)Marshal.SizeOf(sInfo), IntPtr.Zero, 0, ref dwWritten, IntPtr.Zero);            
            CloseHandle(h);            
        }