Couple of times I got a question to <Enable or Disable “Enable write caching on disk” behavior on disk>, How to do it programmatically on Windows? When I got this question for the first time, it was tough but doing research I was able to solve it and it works well. Every next time, it was easy :)

In this post, I will not discuss what exactly this feature does and pros and cons of enable/disable it. I will only discuss, How to do it.

You can do it manually as well.

#1, Select a volume from Explorer, right click –> Properties

#2, Select “Hardware” tab, select disk and click “Properties” button

#3, Select “Policies” tab.

#4, Check/Uncheck to enable/disable “write caching on the disk”

To do it programmatically.

#1, You will need to work with below APIs and control code.

CreateFile Function

DeviceIoControl Function

DISK_CACHE_INFORMATION Structure

IOCTL_DISK_GET_CACHE_INFORMATION Control Code

IOCTL_DISK_SET_CACHE_INFORMATION Control Code

The information is actually gets stored in below registry key, I would not recommend to look for the value in the key directly and design your application on that. It may change in future.

HKLM\SYSTEM\CurrentControlSet\Enum\IDE\Diskxxxxxxxxxxxx\DeviceParameters\Disk
Key : UserWriteCacheSetting

where xxxxxxx is manufacturer information.

The sample will look like below. This is just a test sample and provided only to demonstrate the functionality. You might need to use put more error handling and test the code as you do for regular production environment code.

//////////////////////SAMPLE CODE 
///////////////////////////////////////////////////////////
#define _WIN32_WINNT 0x0503

#include <windows.h>

DISK_CACHE_INFORMATION info;
DISK_CACHE_INFORMATION rinfo;


void main(void)
{
    DWORD rr;
    HANDLE hDevice;
    DWORD err;
    DWORD returned;

    hDevice = CreateFile("\\\\.\\C:", // drive to open
                GENERIC_READ | GENERIC_WRITE,
                FILE_SHARE_WRITE | FILE_SHARE_READ, 
                // share mode
                NULL, // default security attributes
                OPEN_EXISTING, // disposition
                FILE_ATTRIBUTE_SYSTEM, // file attributes
                NULL); // do not copy file attributes
    if(hDevice==INVALID_HANDLE_VALUE)
    {
        return;
    }

    rr = DeviceIoControl(hDevice,IOCTL_DISK_GET_CACHE_INFORMATION,NULL,
                        0,(LPVOID)&info,(DWORD)sizeof(info),(LPDWORD)&returned,    (LPOVERLAPPED)NULL);
    if (!rr)
    {
        err = GetLastError();
        return;
    }

    info.WriteCacheEnabled = true;
    info.ReadCacheEnabled = false;
    info.DisablePrefetchTransferLength = 1;

    rr = DeviceIoControl(hDevice,IOCTL_DISK_SET_CACHE_INFORMATION,(LPVOID)&info,(DWORD)sizeof(info),
                        NULL,0,(LPDWORD)&returned,(LPOVERLAPPED)NULL);
    if (!rr)
    {
        err = GetLastError();
        return;
    }

    rr = DeviceIoControl(hDevice,IOCTL_DISK_GET_CACHE_INFORMATION,NULL,0,
                        (LPVOID)&rinfo,(DWORD)sizeof(rinfo),(LPDWORD)&returned,(LPOVERLAPPED)NULL);
    if (!rr)
    {
        err = GetLastError();
        return;
    }

    CloseHandle(hDevice);
}
//////////////////////SAMPLE CODE 
///////////////////////////////////////////////////////////

*Note—Not all disks and controllers implements write disk caching, I have not tested the behavior or any such disk yet, so behavior is unknown to me.

Nitin Dhawan

Windows SDK - Microsoft