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=-2.7 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,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 3C179C433DB for ; Wed, 17 Feb 2021 08:53:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D36B760C40 for ; Wed, 17 Feb 2021 08:53:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232038AbhBQIx4 (ORCPT ); Wed, 17 Feb 2021 03:53:56 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33180 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229459AbhBQIxx (ORCPT ); Wed, 17 Feb 2021 03:53:53 -0500 Received: from mail-ua1-x934.google.com (mail-ua1-x934.google.com [IPv6:2607:f8b0:4864:20::934]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C6722C061574 for ; Wed, 17 Feb 2021 00:53:12 -0800 (PST) Received: by mail-ua1-x934.google.com with SMTP id n11so2835202uap.10 for ; Wed, 17 Feb 2021 00:53:12 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=5jOsamckWNjO9AHxBIuLZbQoCQ6fAozjYX66GZLvOB0=; b=jTnGrPWsFhJqq+EWqX8IShazDY1r7kYZMv5SfA0GOvEvUD4D/0zaCzBCvEDGtZqUh4 y1xzu/m9IGFGPx4L7LWy/NjgTkkvS7nQ03JKx8Khv+nrR6S/KgOR/A7N8F/hCYSAqTwW asbkGtGE467s9Vzel7uyVvFq89RsI5PUYsWl3AeqYPqw4TbLTe/e5r6IOmNWaBv6FkX/ m2EA+ECYkrOFqTXs6ymmPTJBw3xa/QnG9hxhwi5lxR4iSeDf8Uk3Cn9hdupAcRUUZwEv 8ut8J1dg1gt+Xp7ueWrMOD8IhoV6cl4yiWz7Xiv2qh5FIUMaDzYlsyt4VOej/q/+gYYJ 89eg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=5jOsamckWNjO9AHxBIuLZbQoCQ6fAozjYX66GZLvOB0=; b=ZlmlhCRDPofCR5lHoTRGzsAxe/W+aDMzRL32OCE5L49sfLILClwfMn6YAp9uZu7Ypg kdEimYVacstmfJ6U5Rxqpdrn2KFCZTJKznkjQLPbqVl6HckLlScLAYr4wjUd2IHWQNrw 7r99GJ/ayj6rLx5qL6ZhDw5dtrBdoPSN/IzD/wTCFZNL95UYc6qLiTL2qsKVJhJaxdXS Vq17iwl31/dA0F0lvFJ4tVqG6GB8XkRs3Cn8RIgCi/94U3CCYXLJkY6nRXYSR8O6x1RC 0k9t6YHhqnK7dd7QaptZilQzP2/KmyImtbaN+S9/vcUSU58rmBorA48eF9dV+0DBEnFe tyhA== X-Gm-Message-State: AOAM532FUwIQvZ4/7g1Wis0Dn1bM3WQCMF+AIxHOckT6+oQF8RhG06Rr 0sWwq8EyrVS7QClZcvMgzSpIIXNbJuRqTL78jWpHYVlMlXY= X-Google-Smtp-Source: ABdhPJw30EQmsjVzJzO9bc2UkREZ0txSvEo9gQBAswk/P+ihqNpF/j9vwfgMAYW97FOl/sgeR9zLonhWjYfqNQJHVMM= X-Received: by 2002:ab0:6614:: with SMTP id r20mr13975930uam.68.1613551991171; Wed, 17 Feb 2021 00:53:11 -0800 (PST) MIME-Version: 1.0 References: <20210217110923.62fd685f@natsu> In-Reply-To: <20210217110923.62fd685f@natsu> From: d tbsky Date: Wed, 17 Feb 2021 16:52:59 +0800 Message-ID: Subject: Re: use ssd as write-journal or lvm-cache? To: Roman Mamedov Cc: linux-raid@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-raid@vger.kernel.org Roman Mamedov > > On Wed, 17 Feb 2021 11:27:58 +0800 > Why not both? It's not like you have to use the entire SSD for one or the > other. And it's very unlikely anything will be bottlenecked by concurrent > access to the SSD from both mechanisms. if I use both, then data may write twice to the same ssd, it seems waste. > Choosing one, I would prefer LVM caching, since it also gives benefit for > reads. And the mdadm write journal feature sounds[1] more like of a > reliability, not a performance enhancement. at final stage data write to disk with any kind of cache. so if the data can write to disk with optimized method, it seems speed up the whole thing. read-cache is fine, but I don't know how much benefit it will bring. > In any case, in order to not add a single point of failure to the array, > better rely not on SSD being a "datacenter" one (anything can fail), but use a > RAID1 of two SSDs. yes raid1 is must. "datacenter" ssd can protect the ssd-cache so it won't suffer with power outage. so I think I can enable write-back mode safely.