Fast IO Disallowed

[mca63]

Fast IO Disallowed

Error on an .lck file in a shared folder on Vista Business

What does that means.

[DigeratiPrime]

Basic Idea

Fast IO = A means of reading or writing a cached file without going through the work of generating I/O request packet (IRP).

IRPs Are Different From Fast I/O

http://msdn.microsoft.com/en-us/library/ms790753.aspx

IRPs are the default mechanism for requesting I/O operations. IRPs can be used for synchronous or asynchronous I/O, and for cached or noncached I/O. IRPs are also used for paging I/O. The Memory Manager processes page faults by sending appropriate IRPs to the file system.

Fast I/O is specifically designed for rapid synchronous I/O on cached files. In fast I/O operations, data is transferred directly between user buffers and the system cache, bypassing the file system and the storage driver stack. (Storage drivers do not use fast I/O.) If all of the data to be read from a file is resident in the system cache when a fast I/O read or write request is received, the request is satisfied immediately. Otherwise, a page fault can occur, causing one or more IRPs to be generated. When this happens, the fast I/O routine either returns FALSE, or puts the caller into a wait state until the page fault is processed. If the fast I/O routine returns FALSE, the requested operation failed and the caller must create an IRP.

File systems are required to support IRPs, but they are not required to support fast I/O. When the I/O Manager receives a request for synchronous file I/O (other than paging I/O), it first determines whether the target device object's driver contains an appropriate fast I/O callback routine. If it does, the I/O Manager invokes the fast I/O routine. If no such fast I/O routine is found, the I/O Manager creates and sends an IRP instead.

File system filter drivers are not required to support I/O on control device objects. However, filter device objects that are attached to file systems or volumes are required to pass all unrecognized or unwanted IRPs to the next-lower driver on the driver stack. In addition, filter device objects that are attached to volumes must implement FastIoDetachDevice.