Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261232AbVEQDbC (ORCPT ); Mon, 16 May 2005 23:31:02 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261310AbVEQDbB (ORCPT ); Mon, 16 May 2005 23:31:01 -0400 Received: from shawidc-mo1.cg.shawcable.net ([24.71.223.10]:58082 "EHLO pd2mo3so.prod.shaw.ca") by vger.kernel.org with ESMTP id S261233AbVEQDax (ORCPT ); Mon, 16 May 2005 23:30:53 -0400 Date: Mon, 16 May 2005 21:29:47 -0600 From: Robert Hancock Subject: Re: Disk write cache (Was: Hyper-Threading Vulnerability) In-reply-to: <44PRr-6mz-33@gated-at.bofh.it> To: linux-kernel Message-id: <4289652B.7020408@shaw.ca> MIME-version: 1.0 Content-type: text/plain; format=flowed; charset=ISO-8859-1 Content-transfer-encoding: 7bit X-Accept-Language: en-us, en References: <43Bnu-Ut-9@gated-at.bofh.it> <44sLm-3Mg-33@gated-at.bofh.it> <44sUX-42h-11@gated-at.bofh.it> <44teb-4fb-1@gated-at.bofh.it> <44uaj-4Z3-5@gated-at.bofh.it> <44LXu-2W6-15@gated-at.bofh.it> <44OVj-5xS-3@gated-at.bofh.it> <44PRr-6mz-33@gated-at.bofh.it> User-Agent: Mozilla Thunderbird 1.0.2 (Windows/20050317) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1789 Lines: 35 Richard B. Johnson wrote: > Then I suggest you never use such a drive. Anything that does this, > will end up replacing a good track with garbage. Unless a disk drive > has a built-in power source such as super-capacitors or batteries, what > happens during a power-failure is that all electronics stops and > the discs start coasting. Eventually the heads will crash onto If the power to the drive is truly just cut, then this is basically what will happen. However, I have heard, for what it's worth, that in many cases if you pull the AC power from a typical PC, the Power Good signal from the PSU will be de-asserted, which triggers the Reset line on all the buses, which triggers the ATA reset line, which triggers the drive to finish writing out the sector it is doing. There is likely enough capacitance in the power supply to do that before the voltage drops off. > the platter. Older discs had a magnetically released latch which would > send the heads to an inside landing zone. Nobody bothers anymore. Sure they do. All current or remotely recent drives (to my knowledge, anyway) will park the heads properly at the landing zone on power-off. If the drive is told to power off cleanly, this works as expected, and if the power is simply cut, the remaining energy in the spinning platters is used like a generator to provide power to move the head actuator to the park positon. -- Robert Hancock Saskatoon, SK, Canada To email, remove "nospam" from hancockr@nospamshaw.ca Home Page: http://www.roberthancock.com/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/