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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9D480C352A1 for ; Sat, 3 Dec 2022 05:52:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230315AbiLCFwZ (ORCPT ); Sat, 3 Dec 2022 00:52:25 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47194 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230144AbiLCFwX (ORCPT ); Sat, 3 Dec 2022 00:52:23 -0500 Received: from www18.qth.com (www18.qth.com [69.16.238.59]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0A740DE5D7 for ; Fri, 2 Dec 2022 21:52:22 -0800 (PST) Received: from [73.207.192.158] (port=34144 helo=jpo) by www18.qth.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1p1LRm-0008TV-6v for linux-raid@vger.kernel.org; Fri, 02 Dec 2022 23:52:22 -0600 Date: Sat, 3 Dec 2022 05:52:20 +0000 From: David T-G To: Linux RAID list Subject: stripe size checking (was "Re: about linear and about RAID10") Message-ID: <20221203055220.GS19721@jpo> Reply-To: Linux RAID list References: <20221123220736.GD19721@jpo> <20221124032821.628cd042@nvm> <20221124211019.GE19721@jpo> <512a4cdd-9013-e158-7c77-7409cd0dc3a1@youngman.org.uk> <20221125133050.GH19721@jpo> <20221128144630.GN19721@jpo> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - www18.qth.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - justpickone.org X-Get-Message-Sender-Via: www18.qth.com: authenticated_id: dmail@justpickone.org X-Authenticated-Sender: www18.qth.com: dmail@justpickone.org X-Source: X-Source-Args: X-Source-Dir: Precedence: bulk List-ID: X-Mailing-List: linux-raid@vger.kernel.org Roger, et al -- ...and then Roger Heflin said... % How big is your stripe size set to? The bigger the stripe size on the % md40 main raid the closer it gets to linear. I don't know ... and I don't know how to tell. davidtg@jpo:~> sudo mdadm -D /dev/md40 /dev/md40: Version : 1.2 Creation Time : Mon Aug 8 12:15:12 2022 Raid Level : raid0 Array Size : 3906488320 (3.64 TiB 4.00 TB) Raid Devices : 2 Total Devices : 2 Persistence : Superblock is persistent Update Time : Mon Aug 8 12:15:12 2022 State : clean Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0 Layout : -unknown- Chunk Size : 512K Consistency Policy : none Name : jpo:40 (local to host jpo) UUID : 4735f53c:7cdf7758:e212bec6:aa2942e8 Events : 0 Number Major Minor RaidDevice State 0 9 41 0 active sync /dev/md/md41 1 9 42 1 active sync /dev/md/md42 davidtg@jpo:~> sudo mdadm -E /dev/md40 /dev/md40: MBR Magic : aa55 Partition[0] : 4294967295 sectors at 1 (type ee) Is it the 512k chunk size? % % And I think I did miss one behavior that explains it being faster with % larger, and not sucking as bad as I expected. On disks the internal cache % is supposed to cache the entire track as it goes under the head, so when Sounds familiar. % you ask for the data theoriticaly requiring a seek the drive may already % have the data still in its cache and hence not need to do a seek. The % performance would then be ok so long as the data is still in the cache. Right. Everything is awesome when the data is cached :-) % But given your tests md40 at best gets close to the underlying raids % performance. When linear the underlying performance should be roughly % equal. Now that I understand linear, that makes sense. Thanks again & HANN :-D -- David T-G See http://justpickone.org/davidtg/email/ See http://justpickone.org/davidtg/tofu.txt