Enable or Disable “Enable write caching on disk” behavior on disk

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.

    1: //////////////////////SAMPLE CODE 
    2: ///////////////////////////////////////////////////////////
    3: #define _WIN32_WINNT 0x0503
    4:  
    5: #include <windows.h>
    6:  
    7: DISK_CACHE_INFORMATION info;
    8: DISK_CACHE_INFORMATION rinfo;
    9:  
   10:  
   11: void main(void)
   12: {
   13:     DWORD rr;
   14:     HANDLE hDevice;
   15:     DWORD err;
   16:     DWORD returned;
   17:  
   18:     hDevice = CreateFile("\\\\.\\C:", // drive to open
   19:                 GENERIC_READ | GENERIC_WRITE,
   20:                 FILE_SHARE_WRITE | FILE_SHARE_READ, 
   21:                 // share mode
   22:                 NULL, // default security attributes
   23:                 OPEN_EXISTING, // disposition
   24:                 FILE_ATTRIBUTE_SYSTEM, // file attributes
   25:                 NULL); // do not copy file attributes
   26:     if(hDevice==INVALID_HANDLE_VALUE)
   27:     {
   28:         return;
   29:     }
   30:  
   31:     rr = DeviceIoControl(hDevice,IOCTL_DISK_GET_CACHE_INFORMATION,NULL,
   32:                         0,(LPVOID)&info,(DWORD)sizeof(info),(LPDWORD)&returned,    (LPOVERLAPPED)NULL);
   33:     if (!rr)
   34:     {
   35:         err = GetLastError();
   36:         return;
   37:     }
   38:  
   39:     info.WriteCacheEnabled = true;
   40:     info.ReadCacheEnabled = false;
   41:     info.DisablePrefetchTransferLength = 1;
   42:  
   43:     rr = DeviceIoControl(hDevice,IOCTL_DISK_SET_CACHE_INFORMATION,(LPVOID)&info,(DWORD)sizeof(info),
   44:                         NULL,0,(LPDWORD)&returned,(LPOVERLAPPED)NULL);
   45:     if (!rr)
   46:     {
   47:         err = GetLastError();
   48:         return;
   49:     }
   50:  
   51:     rr = DeviceIoControl(hDevice,IOCTL_DISK_GET_CACHE_INFORMATION,NULL,0,
   52:                         (LPVOID)&rinfo,(DWORD)sizeof(rinfo),(LPDWORD)&returned,(LPOVERLAPPED)NULL);
   53:     if (!rr)
   54:     {
   55:         err = GetLastError();
   56:         return;
   57:     }
   58:  
   59:     CloseHandle(hDevice);
   60: }
   61: //////////////////////SAMPLE CODE 
   62: ///////////////////////////////////////////////////////////

*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