From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D2EE0C433B4 for ; Tue, 18 May 2021 23:48:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B7DAC61074 for ; Tue, 18 May 2021 23:48:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231148AbhERXto (ORCPT ); Tue, 18 May 2021 19:49:44 -0400 Received: from smtp.hosts.co.uk ([85.233.160.19]:40182 "EHLO smtp.hosts.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229969AbhERXto (ORCPT ); Tue, 18 May 2021 19:49:44 -0400 Received: from host109-154-217-227.range109-154.btcentralplus.com ([109.154.217.227] helo=[192.168.1.65]) by smtp.hosts.co.uk with esmtpa (Exim) (envelope-from ) id 1lj9Ro-000CkF-BG; Wed, 19 May 2021 00:48:24 +0100 Subject: Re: raid10 redundancy To: Phillip Susi Cc: Roy Sigurd Karlsbakk , Linux Raid References: <2140221131.2872520.1620837067395.JavaMail.zimbra@karlsbakk.net> <87a6oyr64b.fsf@vps.thesusis.net> <3f3fd663-77e4-8c23-eb22-1b8223eaf277@turmel.org> <87y2ch4c3w.fsf@vps.thesusis.net> <947223877.4161967.1621003717636.JavaMail.zimbra@karlsbakk.net> <87cztpm68z.fsf@vps.thesusis.net> <60A2EC87.9080701@youngman.org.uk> <874kf0yq31.fsf@vps.thesusis.net> From: antlists Message-ID: Date: Wed, 19 May 2021 00:48:26 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <874kf0yq31.fsf@vps.thesusis.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-raid@vger.kernel.org On 18/05/2021 17:05, Phillip Susi wrote: > > Wols Lists writes: > >> When rebuilding a mirror (of any sort), one block written requires ONE >> block read. When rebuilding a parity array, one block written requires >> one STRIPE read. > > Again, we're in agreement here. What you keep ignoring is the fact that > both of these take the same amount of time, provided that you are IO bound. > And if you've got spinning rust, that's unlikely to be true. I can't speak for SATA, but on PATA I've personally experienced the exact opposite. Doubling the load on the interface absolutely DEMOLISHED throughput, turning what should have been a five-minute job into a several-hours job. And if you've got many drives in your stripe, who's to say that won't overwhelm the i/o bandwidth. Your reads could be 50% or less of full speed, because there isn't the back end capacity to pass them on. Cheers, Wol