Write Raw data to hdd

[Carlotto]

Hello,
I can access a physical device to read a specific sector in a USB hard drive.
But my question is how can I Write to a specific sector?
Lets say I want to replace what is in a specific sector of a hard drive with a new data.
Can anyone help me get started, tips, hints, where to look?

Thanks.

[Carlotto]

Here is what I have. The reading part is working by selecting what sector to read, but if I want to write all 0's to one specific sector how do I do that?
I have tried so much but cant figure it out, any tips/help is greatly appreciated.
Thanks.

#include <windows.h>
#include <stdio.h>
#include <iostream>
#include <iomanip>
#include <fstream>
using namespace std;

#define FILE_SHARE_VALID_FLAGS 0x00000007

short Sect
(const char *_dsk, // disk to access
char *&_buff, // buffer where sector will be stored
unsigned int _nsect // sector number, starting with 0
)
{
DWORD dwRead;
DWORD dwWrite;

HANDLE hDisk=CreateFile(_dsk,GENERIC_READ,FILE_SHARE_VALID_FLAGS,0,OPEN_EXISTING,0,0);
if(hDisk==INVALID_HANDLE_VALUE) // this may happen if another program is already reading from disk
{
CloseHandle(hDisk);
cout<<"Incorrect File Handle"<<endl;
return 1;
}
SetFilePointer(hDisk,_nsect*512LL,0,FILE_BEGIN); // which sector to read
ReadFile(hDisk,_buff,512LL,&dwRead,0); // read sector
cout<<"correct File Handle Read"<<endl;
CloseHandle(hDisk);

hDisk=CreateFile(_dsk,GENERIC_WRITE,FILE_SHARE_VALID_FLAGS,0,OPEN_EXISTING,0,0);
if(hDisk==INVALID_HANDLE_VALUE) // this may happen if another program is already reading from disk
{
CloseHandle(hDisk);
cout<<"Incorrect File Handle"<<endl;
return 1;
}

SetFilePointer(hDisk,2*512LL,0,FILE_BEGIN); // which sector to write
WriteFile(hDisk,_buff,512LL,&dwWrite,NULL); // write sector
cout<<"correct File Handle Write"<<endl;
CloseHandle(hDisk);

return 0;
}

int main()
{
char *dsk="\\\\.\\PhysicalDrive1";
int sector=280; //Sector to read/write

char *buff=new char[512LL];
Sect(dsk,buff,sector);

cout << buff << endl; //To see what is inside the buffer

getchar();
}

[VictorN]

Please, use Code tags, not the QUOTE ones!

[2kaud]

SetFilePointer(hDisk,2*512LL,0,FILE_BEGIN); // which sector to write
WriteFile(hDisk,_buff,512LL,&dwWrite,NULL); // write sector

Isn't all you need here is to set the contents of _buff to all 0's first? eg

memset(_buff, 0, 512);

Also you are not checking API return values for failure. ie WriteFile() returns 0 on failure for synchronous write. See https://msdn.microsoft.com/en-us/lib...=vs.85%29.aspx

[OReubens]

Can't do this while the disk is mounted. Direct low level write access to disks requires them to be unmounted.
This may or may not work on special volumes like raid stacks.
For "moving" data around for a disk optimizer, Windows provides API's to do this while the disk is in use (though limited to not allowing to move clusters involved with directories, the MFT and the paging file (there's a few other special cases I can't recall off the top of my head)).


Note that depending on the driver, you may have to make sure the buffer you pass is aligned to a proper address (this could require an address multiple of 512, but could also require page (4k) or larger alignment.
Look up the information on the driver.
For regular harddisks, you typically need page (4k) aligned buffers.

Note that simply writing sectors without knowing what you're doing could destroy the hardisk (or rather make it permanently inaccessible from windows) or really mess up the file system.

also zeroing the disk may be totally pointless on a SSD because here the internal hardware of the SSD will reorganise sectors to reduce wear on flash memory, and writing a sector may not actually erase whatver was there, rather, merely move the allocation to another sector leaving the actual data still available (though not directly accessible via the OS) when using specialised tools.

[Carlotto]

This might be a noobish question, but how can I unmount the drive/disk.

[OReubens]

to unmount D, open a command prompt as administrator

MountVol D: /p