Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264767AbTIDHY6 (ORCPT ); Thu, 4 Sep 2003 03:24:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264769AbTIDHY5 (ORCPT ); Thu, 4 Sep 2003 03:24:57 -0400 Received: from mail.dt.e-technik.Uni-Dortmund.DE ([129.217.163.1]:4495 "EHLO mail.dt.e-technik.uni-dortmund.de") by vger.kernel.org with ESMTP id S264767AbTIDHYz (ORCPT ); Thu, 4 Sep 2003 03:24:55 -0400 Date: Wed, 3 Sep 2003 13:47:14 +0200 From: Matthias Andree To: linux-kernel@vger.kernel.org Cc: Larry McVoy , "Brown, Len" , Giuliano Pochini , Larry McVoy Subject: Re: Scaling noise Message-ID: <20030903114714.GH27875@merlin.emma.line.org> Mail-Followup-To: linux-kernel@vger.kernel.org, Larry McVoy , "Brown, Len" , Giuliano Pochini , Larry McVoy References: <20030903111934.GF10257@work.bitmover.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20030903111934.GF10257@work.bitmover.com> User-Agent: Mutt/1.5.4i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1560 Lines: 31 On Wed, 03 Sep 2003, Larry McVoy wrote: > Expecting more bandwidth to help your app is like expecting more platter > speed to help your file system. It's not the platter speed, it's the > seeks which are the problem. Same thing in system doesn't, it's not the > bcopy speed, it's the cache misses that are the problem. More bandwidth > doesn't do much for that. Platter speed IS a problem for random access involving seeks, because platter speed reduces the rotational latency. Whether it takes 7.1 ms average for a block to rotate past the heads in your average notebook 4,200/min drive or 2 ms in your 15,000/min drive does make a difference. Even if the drive knows where the sectors are and folds rotational latency into positioning latency to the maximum possible extent, for short seeks (track-to-track) it's not going to help. Unless you're going to add more heads or use other media than spinning disc, that is. However, head positioning times, being a tradeoff between noise and speed, aren't that good particularly with many of the quieter drives, so the marketing people use the enormous sequential data rate on outer tracks for advertising. Head positioning time hasn't improved to the extent throughput has, but that doesn't mean higher rotational frequency is useless for random access delays. - 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/