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Message-ID: <4615160A.4090506@cfl.rr.com> Date: Thu, 05 Apr 2007 11:30:18 -0400 From: Phillip Susi <psusi@....rr.com> To: Mark Lord <lkml@....ca> CC: Chris Snook <csnook@...hat.com>, Paa Paa <paapaa125@...mail.com>, linux-kernel@...r.kernel.org Subject: Re: Lower HD transfer rate with NCQ enabled? Mark Lord wrote: > The drive firmware readahead is inherently *way* more effective than > other forms, and without it, sequential read performance really suffers. > Regardless of how software tries to compensate. Why? As the platter spins under the head, the drive can either read or ignore the data. As long as it keeps reading the track, it can't go any faster. Whether in response to its own readahead or to the request queue from the host, either way it should read the data. If its own readahead is faster, then either the host must not be properly performing readahead and keeping the drive request queue filled with sequential requests, or the drive firmware must be broken and decides to ignore the data as it passes under the head, and instead go back to pick it up on the next rotation. > This is mostly a problem with the WD Raptor drive, and some other WD > drives. > I have not yet encountered/noticed the problem with other brands. Sounds like this is a serious bug in the WD firmware. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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