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=-5.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 46F9CC433E2 for ; Fri, 28 Aug 2020 20:39:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1CCDA2074A for ; Fri, 28 Aug 2020 20:39:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="M/stZdmq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726321AbgH1Ujr (ORCPT ); Fri, 28 Aug 2020 16:39:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57102 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726033AbgH1Ujr (ORCPT ); Fri, 28 Aug 2020 16:39:47 -0400 Received: from mail-ot1-x330.google.com (mail-ot1-x330.google.com [IPv6:2607:f8b0:4864:20::330]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 04E75C061264 for ; Fri, 28 Aug 2020 13:39:47 -0700 (PDT) Received: by mail-ot1-x330.google.com with SMTP id h17so337039otl.9 for ; Fri, 28 Aug 2020 13:39:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-transfer-encoding:content-language; bh=o4EKVUxu4E8V2Uo+4VaNnZYt0CpgHvnR22lh1CuI97k=; b=M/stZdmqYejmxbvn/UcY7YilCWxh+rQx2RqB3oLwCSjFqn+TDa92E9aiX3c7J8gV84 W2V6Y4Lr5PMG5e+2MEaYpgoqG/EadrszcXl8omDf0zz2I22h40kyz0US2X+xHajFcdf4 kQnGuQMyHBA2YMOMYcH/mUKo+xX+nT28eNAtLPTzOHcKUv8VbqlRaXSJg0MjpVh9SlH5 HHVXx9YXKv6mSQ3FdaD2uHvZMrm/U4whydV3i0UJPZ4nle9ZttELq6cayFypLaKfVuti TW5Qxk//XvdFRqHb1mp31RKRVvpnvm4XmeJ8asb0zzdTEQl0+GDQ8p/q3qUZ+HPSVZtJ puKQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :content-language; bh=o4EKVUxu4E8V2Uo+4VaNnZYt0CpgHvnR22lh1CuI97k=; b=V/JZgmv4rGCqNN44mlaH2Z+VuCFCqI/4P02Gh9/NpsE3Ze7mwIfrBuPiR0erGZQRRk PcgSsR/0Nwbs2u5C2Zds6+0loppNx6sztSs6Bm2y4UvGT4vS9YP9XOAC/lkef9Zn81L1 Bl5yySjb2tzR/m6avRyFs8Q4xFLNjFwlpkjphC/BhENRmXDZOgy7bSnzq/c3nHcc47c7 P55GY0bXAEvq7Tkge1pfJxfbh6DopAbojxawv5vC5YwVFuORDD1fZDAXL6e1Bx5vL3kA 3Cv31I+2L/44tLA+hVuI+FH40271W49w+1zZ7TI9CUs9+Jkp4MGqA8wjcriJzX7UVT2V mxlQ== X-Gm-Message-State: AOAM5316dWwSvEM4O8d8n3n8F+zy+uVHLaPEs6wGAuIYqQzZgWuXt1Fj ZCqj0RKMqpbasLewM4zaEge836epP7o= X-Google-Smtp-Source: ABdhPJzMjKPCrP2MHkr71EVQXWDtWKLaoAMdjK18cNe0tQkX6AgqClr0a3fD43MkWh8s7VMWHjQeMQ== X-Received: by 2002:a9d:5f0c:: with SMTP id f12mr297966oti.141.1598647186156; Fri, 28 Aug 2020 13:39:46 -0700 (PDT) Received: from [192.168.3.65] ([47.187.193.82]) by smtp.googlemail.com with ESMTPSA id w11sm127299oog.33.2020.08.28.13.39.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 28 Aug 2020 13:39:45 -0700 (PDT) Subject: Re: Best way to add caching to a new raid setup. To: Roman Mamedov , "R. Ramesh" Cc: Linux Raid References: <16cee7f2-38d9-13c8-4342-4562be68930b.ref@verizon.net> <16cee7f2-38d9-13c8-4342-4562be68930b@verizon.net> <20200828224616.58a1ad6c@natsu> From: Ram Ramesh Message-ID: <448afb39-d277-445f-cc42-2dfc5210da7b@gmail.com> Date: Fri, 28 Aug 2020 15:39:45 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200828224616.58a1ad6c@natsu> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-raid-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-raid@vger.kernel.org On 8/28/20 12:46 PM, Roman Mamedov wrote: > On Thu, 27 Aug 2020 21:31:07 -0500 > "R. Ramesh" wrote: > >> I have two raid6s running on mythbuntu 14.04. The are built on 6 >> enterprise drives. So, no hd issues as of now. Still, I plan to upgrade >> as it has been a while and the size of the hard drives have become >> significantly larger (a indication that my disks may be older) I want to >> build new raid using the 16/14tb drives. Since I am building new raid, I >> thought I could explore caching options. I see a mention of LVM cache >> and few other bcache/xyzcache etc. > Once you set up bcache, it cannot be removed. The volume will always stay a > bcache volume, even if you decide to stop using caching. Which feels weird and > potentially troublesome, going through an extra layer (kernel driver) with its > complexity and computational overhead (no matter how small). > > On the other hand LVM with caching turned off is just normal LVM, that you'd > likely would have used anyway, for other benefits that it provides. > > Also my impression is that LVM has more solid and reliable codebase, but > bcache might provide a somewhat better the performance boost due to caching. > Thanks for the info on bcache. I do not think it will be my favorite. I am going to try LVM cache as my first choice. Note that the new disks will be spare disks for some time and I will be able to try out a few things before deciding to put it into use. One thing about LVM that I am not clear. Given the choice between creating /mirror LV /on a VG over simple PVs and /simple LV/ over raid1 PVs, which is preferred method? Why? Ramesh