How can I/O priority of a process be increased?

Question

I want to increase the I/O priority of a process. Answers for both .NET and Windows Vista would be nice. processexplorer is ok as well.

Answer 1

The relevant information seems to be a bit scattered compared to the usual MS documentation. There is this white paper that discusses I/O Prioritization in windows. This doc seems to have beta flags all over it but I guess it's probably mostly pretty accurate.

Two important things to note:

1. You can only reduce the priority of IO requests below normal.
2. The driver can ignore any such request and treat it as normal anyway.

The useful APIs for client applications are SetFileInformationByHandle:

FILE_IO_PRIORITY_HINT_INFO priorityHint;
priorityHint.PriorityHint = IoPriorityHintLow;
result = SetFileInformationByHandle( hFile,
                                     FileIoPriorityHintInfo,
                                     &priorityHint,
                                     sizeof(PriorityHint));

SetPriorityClass:

// reduce CPU, page and IO priority for the whole process
result = SetPriorityClass( GetCurrentProcess(),
                           PROCESS_MODE_BACKGROUND_BEGIN);
// do stuff
result = SetPriorityClass( GetCurrentProcess(),
                           PROCESS_MODE_BACKGROUND_END);

SetThreadPriority which is similar:

// reduce CPU, page and IO priority for the current thread
SetThreadPriority(GetCurrentThread(), THREAD_MODE_BACKGROUND_BEGIN);
// do stuff
SetThreadPriority(GetCurrentThread(), THREAD_MODE_BACKGROUND_END);

SetFileBandwithReservation:

// reserve bandwidth of 200 bytes/sec
result = SetFileBandwidthReservation( hFile,
                                  1000,
                                  200,
                                  FALSE,
                                  &transferSize,
                                  &outstandingRequests );

For .Net do the usual stuff with P/Invoke.