From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from auth-3.ukservers.net ([217.10.138.152]:57546 "EHLO auth-3.ukservers.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751731AbeA3Knm (ORCPT ); Tue, 30 Jan 2018 05:43:42 -0500 Subject: Re: [LSF/MM TOPIC] De-clustered RAID with MD To: NeilBrown , Johannes Thumshirn , lsf-pc@lists.linux-foundation.org References: <5A6F4CA6.5060802@youngman.org.uk> <87fu6o5o83.fsf@notabene.neil.brown.name> Cc: linux-raid@vger.kernel.org, linux-block@vger.kernel.org, Hannes Reinecke , Neil Brown From: Wols Lists Message-ID: <5A704C59.4000705@youngman.org.uk> Date: Tue, 30 Jan 2018 10:43:37 +0000 MIME-Version: 1.0 In-Reply-To: <87fu6o5o83.fsf@notabene.neil.brown.name> Content-Type: text/plain; charset=windows-1252 Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org On 29/01/18 21:50, NeilBrown wrote: > By doing declustered parity you can sanely do raid6 on 100 drives, using > a logical stripe size that is much smaller than 100. > When recovering a single drive, the 10-groups-of-10 would put heavy load > on 9 other drives, while the decluster approach puts light load on 99 > other drives. No matter how clever md is at throttling recovery, I > would still rather distribute the load so that md has an easier job. Not offering to do it ... :-) But that sounds a bit like linux raid-10. Could a simple approach be to do something like "raid-6,11,100", ie raid-6 with 9 data chunks, two parity, striped across 100 drives? Okay, it's not as good as the decluster approach, but it would spread the stress of a rebuild across 20 drives, not 10. And probably be fairly easy to implement. Cheers, Wol