C++ FileApi.h no caching, how do i get the disk activity to 100%

Hello and thanks for reviewing my problem.

I have a system configured with PCIe RAID0 controller x16 lines connected to 4 NVMe Intel drives 2Tb each through m.2 connector. Using ATTO Disk Benchmark application, File size set to 8Gb and block size set to 2Mb the max read rate is ~7Gb/S meanwhile by looking at the task manager the disk activity percentage is at the peak 100% during the process.

My problem: I developed a simple c++ application using the Qt-Creator and MinGW-64bit compiler, using FileApi.h header to open a file with system caching disabled (No Buffering) and read same byte amount (2Mb) from the same file size (8Gb) the result is not even close, the rate is so slow ~1.2Gb/S and the disk activity during the process is around 23%

here is my code:

        #include <fileapi.h>

        void main()
        {
        HANDLE dataFile;

            dataFile = CreateFileA("File.bin", GENERIC_READ, 0, nullptr,
           OPEN_EXISTING,  FILE_ATTRIBUTE_NORMAL | FILE_FLAG_NO_BUFFERING, nullptr);
            FlushFileBuffers(dataFile);
            if (dataFile == INVALID_HANDLE_VALUE)
                return ;

        //Start reading 3000 times from the file
            int counter = 0;
            while(counter < 3000){
                char * buffer = new char [pktSize*sizeof(int)];
                unsigned long read;
                ReadFile(dataFile, buffer, 2097152  /*2 Megabytes */, &read, nullptr);
                counter+=1;
                delete[] buffer;
            }
        }

I appreciate any help or advice and will be super thankful.

Solution

On each iteration you allocate new buffer in memory. It causes large memory traffic and performance degradation. Initialize it once and reuse:

char * buffer = new char [pktSize*sizeof(int)];
while(counter < 3000)
{
  unsigned long read;
  ReadFile(dataFile, buffer, 2097152  /*2 Megabytes */, &read, nullptr);
  counter+=1;
}
delete[] buffer;

Also you should be sure that buffer size pktSize*sizeof(int) is greater than 2097152 /*2 Megabytes */.