How to create fast and efficient filestream writes on large sparse files

Question

I have an application that writes large files in multiple segments. I use FileStream.Seek to position each wirte. It appears that when I call FileStream.Write at a deep position

Answer 1

Here is some code to use sparse files:

using System;
using System.ComponentModel;
using System.IO;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading;

using Microsoft.Win32.SafeHandles;

public static class SparseFiles
{
    private const int FILE_SUPPORTS_SPARSE_FILES = 64;

    private const int FSCTL_SET_SPARSE = 0x000900c4;

    private const int FSCTL_SET_ZERO_DATA = 0x000980c8;

    public static void MakeSparse(this FileStream fileStream)
    {
        var bytesReturned = 0;
        var lpOverlapped = new NativeOverlapped();
        var result = DeviceIoControl(
            fileStream.SafeFileHandle, 
            FSCTL_SET_SPARSE, 
            IntPtr.Zero, 
            0, 
            IntPtr.Zero, 
            0, 
            ref bytesReturned, 
            ref lpOverlapped);

        if (!result)
        {
            throw new Win32Exception();
        }
    }

    public static void SetSparseRange(this FileStream fileStream, long fileOffset, long length)
    {
        var fzd = new FILE_ZERO_DATA_INFORMATION();
        fzd.FileOffset = fileOffset;
        fzd.BeyondFinalZero = fileOffset + length;
        var lpOverlapped = new NativeOverlapped();
        var dwTemp = 0;

        var result = DeviceIoControl(
            fileStream.SafeFileHandle, 
            FSCTL_SET_ZERO_DATA, 
            ref fzd, 
            Marshal.SizeOf(typeof(FILE_ZERO_DATA_INFORMATION)), 
            IntPtr.Zero, 
            0, 
            ref dwTemp, 
            ref lpOverlapped);
        if (!result)
        {
            throw new Win32Exception();
        }
    }

    public static bool SupportedOnVolume(string filename)
    {
        var targetVolume = Path.GetPathRoot(filename);
        var fileSystemName = new StringBuilder(300);
        var volumeName = new StringBuilder(300);
        uint lpFileSystemFlags;
        uint lpVolumeSerialNumber;
        uint lpMaxComponentLength;

        var result = GetVolumeInformationW(
            targetVolume, 
            volumeName, 
            (uint)volumeName.Capacity, 
            out lpVolumeSerialNumber, 
            out lpMaxComponentLength, 
            out lpFileSystemFlags, 
            fileSystemName, 
            (uint)fileSystemName.Capacity);
        if (!result)
        {
            throw new Win32Exception();
        }

        return (lpFileSystemFlags & FILE_SUPPORTS_SPARSE_FILES) == FILE_SUPPORTS_SPARSE_FILES;
    }

    [DllImport("Kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool DeviceIoControl(
        SafeFileHandle hDevice, 
        int dwIoControlCode, 
        IntPtr InBuffer, 
        int nInBufferSize, 
        IntPtr OutBuffer, 
        int nOutBufferSize, 
        ref int pBytesReturned, 
        [In] ref NativeOverlapped lpOverlapped);

    [DllImport("Kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool DeviceIoControl(
        SafeFileHandle hDevice, 
        int dwIoControlCode, 
        ref FILE_ZERO_DATA_INFORMATION InBuffer, 
        int nInBufferSize, 
        IntPtr OutBuffer, 
        int nOutBufferSize, 
        ref int pBytesReturned, 
        [In] ref NativeOverlapped lpOverlapped);

    [DllImport("kernel32.dll", EntryPoint = "GetVolumeInformationW")]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool GetVolumeInformationW(
        [In] [MarshalAs(UnmanagedType.LPWStr)] string lpRootPathName, 
        [Out] [MarshalAs(UnmanagedType.LPWStr)] StringBuilder lpVolumeNameBuffer, 
        uint nVolumeNameSize, 
        out uint lpVolumeSerialNumber, 
        out uint lpMaximumComponentLength, 
        out uint lpFileSystemFlags, 
        [Out] [MarshalAs(UnmanagedType.LPWStr)] StringBuilder lpFileSystemNameBuffer, 
        uint nFileSystemNameSize);

    [StructLayout(LayoutKind.Sequential)]
    private struct FILE_ZERO_DATA_INFORMATION
    {
        public long FileOffset;

        public long BeyondFinalZero;
    }
}

And sample code to test the above class.

class Program
{
    static void Main(string[] args)
    {
        using (var fileStream = new FileStream("test", FileMode.Create, FileAccess.ReadWrite, FileShare.None))
        {
            fileStream.SetLength(1024 * 1024 * 128);
            fileStream.MakeSparse();
            fileStream.SetSparseRange(0, fileStream.Length);
        }
    }
}

Hope this helps