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=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS autolearn=unavailable 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 E94A1C4360F for ; Sat, 30 Mar 2019 13:05:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B755D2146F for ; Sat, 30 Mar 2019 13:05:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ZLwOfUNd" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730832AbfC3NFI (ORCPT ); Sat, 30 Mar 2019 09:05:08 -0400 Received: from mail-ed1-f46.google.com ([209.85.208.46]:42499 "EHLO mail-ed1-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730799AbfC3NFI (ORCPT ); Sat, 30 Mar 2019 09:05:08 -0400 Received: by mail-ed1-f46.google.com with SMTP id x61so4290741edc.9; Sat, 30 Mar 2019 06:05:06 -0700 (PDT) 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=OcIV8+1AC9xA1MsE5GdTUPWNInrXd3mCdewr7SGloZw=; b=ZLwOfUNdm9d8An/bMq7Y7dKq2wqplePCSDW9ufgHkAC1Un3TGqKpZAP2TZPI5AlgkQ nmtWTiCQWlNhALZTpr/uluhwpxbTR+I7Mq/HDY4jOF37AGAM2hq18pDVqhA82CgtiDhL PodDZh9dVsXI9oL4gfu6dLlHQoUGz4E5++Km5ZQNr4b5/WtKHTLn8/sCJaocU8ikhlST 1JoRF4OVSc3k9K02oPdMH9xFrxhqF6YpaCo6pl3Y+sFdTBIksOLD05NODxOHqNkl8/2I +bNn1k5vFsTXkRNBcMMjwg4dDvC4Ndxc2sLZuaU8yCMZ+8lhLwkZurXAv+oG8bwZPDiH MzAA== 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=OcIV8+1AC9xA1MsE5GdTUPWNInrXd3mCdewr7SGloZw=; b=nYZmVjBlPzVR5V0FDzgoUBZuRn5RM7hxcweDW0wXwUcLib8gdXiz0IKmUfBlFCCBrG vspxUS/bb/KEZmDgVHigr9Cc0Tq6JLqTAryTo8WhcIQFn6J6p6i/7taehdQL0v89KK5q zMlAslw9uO32Vdc+eZv+j9W0pUMYetMH+44ok4i5U2ZtvAJY+SZb215jSJUY78IO+t4V pdwkr2MXG0CgQSniH5ow9qJxgxdte+g+GFXWaYsGO7PzQJGfVYbKCVXkiRHYAD/Xokdo Vibj+n8xyNJ9Oi47VTOQOaHTGraf6TUgyd7OGnQYi9kN391YqUWx7/xJjAMq6XCpv0Ia B+IQ== X-Gm-Message-State: APjAAAVxf8VH7SOy+tRUmuFuuSvy7tfvw1ur7TI7fQxIeU2fnBvWh7i6 oB4mDDMO4gxBHMyzKgz2gJOtGlZMkSBhEArfuCWEQeBl X-Google-Smtp-Source: APXvYqzIWrGN2Z+MgiIyarEJVA0E2XcWmvsJ415lOJ21+4GmBzoFAEGyNYnBYON44nvNq5XRSz90g4KaT5em4j/1yKc= X-Received: by 2002:a50:8ba6:: with SMTP id m35mr36746344edm.33.1553951105925; Sat, 30 Mar 2019 06:05:05 -0700 (PDT) MIME-Version: 1.0 References: <16edb2d0-ee41-908f-e0bf-5c27160ccff7@gmx.com> In-Reply-To: <16edb2d0-ee41-908f-e0bf-5c27160ccff7@gmx.com> From: Supercilious Dude Date: Sat, 30 Mar 2019 13:04:54 +0000 Message-ID: Subject: Re: Is it possible that certain physical disk doesn't implement flush correctly? To: Qu Wenruo Cc: "linux-btrfs@vger.kernel.org" , Linux FS Devel , linux-block@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Sat, 30 Mar 2019 at 13:00, Qu Wenruo wrote: > I'm purposing to measure the execution time of flush/fsync, not write. > > And if flush takes 0ms, it means it doesn't really write cached data > onto disk. > That is correct. The controller ignores your flush requests on the virtual disk by design. When the data hits the controller it is considered "stored" - the physical disk(s) storing the virtual disk is an implementation detail. The performance characteristics of these controllers are needed to make big arrays work in a useful manner. My controller is connected to 4 HP 2600 enclosures with 12 drives each. Waiting for a flush on a single disk before continuing work on the remaining 47 disks would be catastrophic for performance. Regards