From owner-freebsd-hackers Tue Oct 29 17:28:26 2002 Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id EE57437B401 for ; Tue, 29 Oct 2002 17:28:24 -0800 (PST) Received: from canning.wemm.org (canning.wemm.org [192.203.228.65]) by mx1.FreeBSD.org (Postfix) with ESMTP id A8AEC43E75 for ; Tue, 29 Oct 2002 17:28:24 -0800 (PST) (envelope-from peter@wemm.org) Received: from wemm.org (localhost [127.0.0.1]) by canning.wemm.org (Postfix) with ESMTP id 8E54B2A88D; Tue, 29 Oct 2002 17:28:24 -0800 (PST) (envelope-from peter@wemm.org) X-Mailer: exmh version 2.5 07/13/2001 with nmh-1.0.4 To: Daniel O'Connor , Chuck Robey , Kenneth Culver , "Wilkinson, Alex" , hackers@FreeBSD.ORG Subject: Re: [hardware] Tagged Command Queuing or Larger Cache ? In-Reply-To: <20021029103133.GA18812@HAL9000.homeunix.com> Date: Tue, 29 Oct 2002 17:28:24 -0800 From: Peter Wemm Message-Id: <20021030012824.8E54B2A88D@canning.wemm.org> Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG David Schultz wrote: > Thus spake Peter Wemm : > > Actually, not even then. Modern IDE drives only write entire tracks at a > > time. If you modify a single sector, then the drive has to read the entire > > track into the buffer, in-place edit the sector, and then rewrite the entir e > > track. > [...] > > And that completely blows FFS's assumptions out of the water. And what > > is sad is that many SCSI disks are similar these days. But not all of > > them (I'm told). > > I've heard this before. It would be very useful to have > information about which drives have this misfeature, but I guess > it isn't the sort of thing that hard drive manufacturers like to > advertise. Does anyone have any data on track-writing drives? IBM used to claim it as a feature and have patents on it. As best as I can tell, all IDE disks have it since about 1999 or so. Quantum and IBM certainly did, as it was a way of getting the drive capacity up and reducing the cost. One way that you can tell is by seeing how big the slowdown is when write caching is turned off and whether you see the same slowdown slowdown regardless of any sector interleaving. ie: if writing to every 10th or 20th (or whatever) sector is just as slow as writing to every sector with write caching turned off, then you have a track-write drive. This is because every single sector write causes the entire track to be written. Cheers, -Peter -- Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com "All of this is for nothing if we don't go to the stars" - JMS/B5 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message