<serviceDebug 
            httpHelpPageEnabled="true" 
            includeExceptionDetailInFaults="true"
          />

using (SqlConnection connection = new SqlConnection(connStringBuilder.ToString()))
            {
                connection.Open();

                SqlCommand command = new SqlCommand("SELECT TOP(1) Photo.PathName(), GET_FILESTREAM_TRANSACTION_CONTEXT() FROM employees", connection);
//понятно, что GET_FILESTREAM_TRANSACTION_CONTEXT  возвращает токен, который представляет текущий контекст транзакции сеанса. Этот токен используется приложением для связывания потоковых операций FILESTREAM файловой системы с транзакцией.
но что конкретно он делает и зачем - не понятно.
                SqlTransaction tran = connection.BeginTransaction(IsolationLevel.ReadCommitted);
                command.Transaction = tran;

                using (SqlDataReader reader = command.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        // Get the pointer for file 
                        string path = reader.GetString(0);//вот тут вообще непонятно откуда какой путь берется
                        byte[] transactionContext = reader.GetSqlBytes(1).Buffer; 

                        // Create the SqlFileStream
                        using (Stream fileStream = new SqlFileStream(path, transactionContext, FileAccess.Write, FileOptions.SequentialScan, allocationSize: 0))
                        {
                            // Write a single byte to the file. This will replace any data in the file.
                            fileStream.WriteByte(0x01); //и вот снова - запись байта!
                        }
                    }
                }
                tran.Commit();
            }

INSERT INTO Archive.dbo.Records
    VALUES (newid (), 3, 
      CAST ('Seismic Data' as varbinary(max)));
GO

public void InsertFile(string fileName)
{
	if (!File.Exists(fileName)) return;
	var content = File.ReadAllBytes(fileNam);
	using(var connection = new SqlConnection("connection string"))
	{
		using(var command = new SqlCommand(connection, "insert into MyFileTable (file_guid, file_content) values (@file_guid, @file_content)"))
		{
			command.Parameters.AddWithValue("@file_guid", Guid.NewGuid());
			command.Parameters.AddWithValue("@file_content", content);
			
			command.ExecuteNonQuery();
		}
	}
}
Вот к чему привела вставка файла в 1,5 Гб...
System.OutOfMemoryException was unhandled
  HResult=-2147024882
  Message=Exception of type 'System.OutOfMemoryException' was thrown.
  Source=mscorlib
  StackTrace:
       at System.IO.File.InternalReadAllBytes(String path, Boolean checkHost)
       at System.IO.File.ReadAllBytes(String path)
       at WindowsFormsApplication1.Form1.button7_Click(Object sender, EventArgs e) in c:\Users\Administrator\Desktop\WindowsFormsApplication1\WindowsFormsApplication1\Form1.cs:line 223
       at System.Windows.Forms.Control.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
       at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ButtonBase.WndProc(Message& m)
       at System.Windows.Forms.Button.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(Form mainForm)
       at WindowsFormsApplication1.Program.Main() in c:\Users\Administrator\Desktop\WindowsFormsApplication1\WindowsFormsApplication1\Program.cs:line 19
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: