From owner-freebsd-hackers@FreeBSD.ORG Fri Aug 19 16:58:15 2005 Return-Path: X-Original-To: freebsd-hackers@freebsd.org 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 49F7116A41F for ; Fri, 19 Aug 2005 16:58:15 +0000 (GMT) (envelope-from julian@elischer.org) Received: from delight.idiom.com (delight.idiom.com [216.240.32.16]) by mx1.FreeBSD.org (Postfix) with ESMTP id 063D043D45 for ; Fri, 19 Aug 2005 16:58:14 +0000 (GMT) (envelope-from julian@elischer.org) Received: from idiom.com (idiom.com [216.240.32.1]) by delight.idiom.com (Postfix) with ESMTP id 941E62090AF; Fri, 19 Aug 2005 09:58:14 -0700 (PDT) Received: from [192.168.2.2] (home.elischer.org [216.240.48.38]) by idiom.com (8.12.11/8.12.11) with ESMTP id j7JGwCKJ000476; Fri, 19 Aug 2005 09:58:13 -0700 (PDT) (envelope-from julian@elischer.org) Message-ID: <43060FA4.5080807@elischer.org> Date: Fri, 19 Aug 2005 09:58:12 -0700 From: Julian Elischer User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7.7) Gecko/20050424 X-Accept-Language: en, hu MIME-Version: 1.0 To: bv@wjv.com References: <20050819120018.206B416A420@hub.freebsd.org> <20050819141130.GB54150@wjv.com> In-Reply-To: <20050819141130.GB54150@wjv.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Cc: freebsd-hackers@freebsd.org Subject: Re: Parking disk drive heads X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 19 Aug 2005 16:58:15 -0000 Bill Vermillion wrote: > "Bits dont fail me now!" was what > freebsd-hackers-request@freebsd.org muttered as he hastily typed > this on Fri, Aug 19, 2005 at 12:00 : > > >> 1. Re: Parking disk drive heads (Glenn Dawson) > > > The setups for parking heads pretty much went away when the move > from MFM drive to ATA technology. Well, they are obvioulsy back as the IBM and apple laptops invoke them. > > And if your are worried about a shock that could damage the drive, > you will probably lose your computer at the same time. not evennearly true, but even if it were, I'd rather lase the laptop and be able to salvage teh drive than lose it all. > > Check the technical specs on current drives. You will see that > most will handled well over 100G shocks when not running, and > usually far over 20G in operational mode. Considering that > 20G to the human body usually means death you aren't going to have > to worry about losing drives to operating bumps unless you have a > habit of dropping them in parachutes from airplanes. :-) this shows a slight misunderstanding of the use of 'G' in describing such events. "shock" Gs are not the same as sustained Gs. If you bang your hand on the table, the cells on the outer side of your skin go from 10 km/h (~2m/s) to 0km/h in 0.000001m (1/1000th of a mm). It takes your cells, traveling at 2m/s about 1/500000 the of a second to cover that distance, so the accelleration is somethign of the order of 2/(1/500000) or, about 1 million Gs. cells a couple of cells in already see significantly lower shocks as the external cells distort, absobing energy, and lengthenning the abount of time that the inner cells have to come to a stop. it's something like an order of magnitude per cell for the first few cells. Shock loading for a two hard objects hitting each other, (e.g. the ground and a laptop) can be in the 100s of thousands of Gs for parts directly attached, to hundreds of G's on indirectly attached items to 10s of G's for shock mounted items such as the disk drive. Moving requirements for survival from 20G to 100G by parking the heads in flight can greatly increase the chances that the drive survives. just placing an unmounted drive down on a hard table, even when not running, can ruin it. We lost hundresds that way at Whistle until we did a failure analysis. Just placing a rubber mat on the table. fixed it and instructing the staff to always put the drives on a soft surface made the problem go right away. > > I have ruined drives with a bad bump in the past - but those > were MFM drives - and that happened in the mid-to-late 1980s. > > The first HDs I saw could withstand less than 1G in shipping so > the 5.25" Shugart ST-505 drives - $25090 for 5MB [that is MegaByte] > were shipped in foam padded boxes a bit larger than the drive, and > these boxes were suspended by springs from the corners of a much > larger shipping box - in the 18"x18" size category. > > IOW - unless you are running some early ATA drives, shocks when > running are something you don't have to really worry about, unless > you plan to shove the entire computer off the desk when it is > running with the power on. > > Bill > > [The orignal post was in of freebsd-hackers Digest, Vol 126, Issue 5] > > >