Jeff Garzik wrote:
NCQ provides for a more asynchronous flow. It helps greatly with reads (of which most are, by nature, synchronous at the app level) from multiple threads or apps. It helps with writes, even with write cache on, by allowing multiple commands to be submitted and/or retired at the same time.
But when writing, what is the difference between queuing multiple tagged writes, and sending down multiple untagged cached writes that complete immediately and actually hit the disk later? Either way the host keeps sending writes to the disk until it's buffers are full, and the disk is constantly trying to commit those buffers to the media in the most optimal order.
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