From mboxrd@z Thu Jan 1 00:00:00 1970 From: Elias Oltmanns Subject: Re: [PATCH 4/4 v2] Add documentation for hard disk shockprotection interface Date: Sat, 20 Sep 2008 00:05:08 +0200 Message-ID: <87ej3f7pwr.fsf@denkblock.local> References: <87d4j2n3dn.fsf@denkblock.local> <20080917163145.9870.8575.stgit@denkblock.local> <1221724782.3261.13.camel@raz> <87iqssmpl0.fsf@denkblock.local> <1221854586.7473.16.camel@raz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from nebensachen.de ([195.34.83.29]:41752 "EHLO mail.nebensachen.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750957AbYITFyy (ORCPT ); Sat, 20 Sep 2008 01:54:54 -0400 In-Reply-To: <1221854586.7473.16.camel@raz> (raz ben yehuda's message of "Fri, 19 Sep 2008 22:03:06 +0200") Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: raz ben yehuda Cc: linux-ide@vger.kernel.org raz ben yehuda wrote: > On Fri, 2008-09-19 at 11:50 +0200, Elias Oltmanns wrote: >> "Raz Ben-Yehuda" wrote: >> > Elias >> > looks very interesting. >> > 1. How will it impact VM , swappers , raids ? >> >> What exactly do you want to know? As long as the disk is parked, you can >> do no I/O on it, i.e. no swapping is possible. Since I don't know >> anything about the implementation of raids and don't have a raid setup >> here, I can't really tell how a raid device will behave exactly when one >> of its disks has been parked. Generally, all I/O will be delayed until >> the disk is unparked again. >> > 2. you said it has no value for servers ? did you try ? >> >> Again, I'm not quite sure what you want to know. Obviously, desktops or >> servers for that matter can have disks installed that support the unload >> feature. On these devices you can use the interface as described in my >> document. All I'm saying is that the interface has been designed with >> laptops in mind because I don't see in which situation immediate head >> unloading would be required or even desirable in a classical server >> environment. > I will rephrase. does head parking increase reliability ( MTBF ... MTTF ) of a disk ? > My servers hardly generate IOs at night times, does head parking at nights extend > the life of a disk ? or is it the opposite ? does it matter ? Disk head parking is meant as a short term emergency resort. In general, it does *not* extend the lifetime of a disk. In fact, emergency head unloads are considered to be costly and smart even counts those events as an aging factor. It really is just a means to prevent even worse damage due to heavy shocks, nothing for regular maintenance. Hope that helps, Elias