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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 D6D14C432C0 for ; Mon, 2 Dec 2019 23:27:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6E96E20715 for ; Mon, 2 Dec 2019 23:27:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=dirtcellar.net header.i=@dirtcellar.net header.b="pclLNFDb" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725919AbfLBX1u (ORCPT ); Mon, 2 Dec 2019 18:27:50 -0500 Received: from smtp.domeneshop.no ([194.63.252.55]:43111 "EHLO smtp.domeneshop.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725834AbfLBX1u (ORCPT ); Mon, 2 Dec 2019 18:27:50 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=dirtcellar.net; s=ds201810; h=Content-Transfer-Encoding:Content-Type: In-Reply-To:MIME-Version:Date:Message-ID:From:References:To:Subject:Reply-To: Sender:Cc:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=+fEuokqGDSQW4L3cFNAiDrH+7vvj7sA2DzLZUB7ylxc=; b=pclLNFDbhaZR/6JLZpQI2iWeKb m0IOacHOqYatp8Zj9AjmDujM9H36n7exa8oQIQ4ksGY2c6ZKH2ulxjMvPUeCdiU35lwZmFscLpIyv 2100ilWoMfLe5aS3iaInyTRkVsU8ET7sAofCMOY5tKRn02wjmq5/WQ6iWICiDQiy3zXxgMYQH3STE rryQFaANN/6EjncGhkTXbC6d/NurgPrcU9RRvNxaIKTHto6Yi/0cKRhyvaL5FC5jm23vN6hoptGxG KFzw3jw5B26jW82lPKhhmH3VWYyt/srJcE1PO5PVd/W8tRONGKd2MCJKdluPCSmHhuTlO4Ir9MrY4 Ib0siURA==; Received: from 254.79-160-170.customer.lyse.net ([79.160.170.254]:42175 helo=[10.0.0.10]) by smtp.domeneshop.no with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1ibv6a-0005f0-38; Tue, 03 Dec 2019 00:27:48 +0100 Reply-To: waxhead@dirtcellar.net Subject: Re: BTRFS subvolume RAID level To: Anand Jain , Btrfs BTRFS References: <494b0df1-2aab-5169-836d-e381498f64db@dirtcellar.net> From: waxhead Message-ID: Date: Tue, 3 Dec 2019 00:27:47 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0 SeaMonkey/2.49.5 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org Anand Jain wrote: > >> I imagine that RAIDc4 for example could potentially give a grotesque >> speed increase for parallel read operations once BTRFS learns to >> distribute reads to the device with the least waitqueue / fastest >> devices. > >  That exactly was the objective of the Readmirror patch in the ML. >  It proposed a framework to change the readmirror policy as needed. > > Thanks, Anand Indeed. If I remember correctly your patch allowed for deterministic reading from certain devices. As just a regular btrfs user the problem I see with this is that you loose a "potential free scrub" that *might* otherwise happen from often read data. On the other hand that is what manual scrubbing is for anyway.