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=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 9AE8CC3A5A0 for ; Mon, 19 Aug 2019 18:37:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7AF98218BA for ; Mon, 19 Aug 2019 18:37:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728168AbfHSShM (ORCPT ); Mon, 19 Aug 2019 14:37:12 -0400 Received: from rin.romanrm.net ([91.121.75.85]:42602 "EHLO rin.romanrm.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728173AbfHSShL (ORCPT ); Mon, 19 Aug 2019 14:37:11 -0400 Received: from natsu (natsu.40.romanrm.net [IPv6:fd39:aa:c499:6515:e99e:8f1b:cfc9:ccb8]) by rin.romanrm.net (Postfix) with SMTP id A18D5202D3; Mon, 19 Aug 2019 18:37:09 +0000 (UTC) Date: Mon, 19 Aug 2019 23:37:09 +0500 From: Roman Mamedov To: Marc MERLIN Cc: linux-block@vger.kernel.org, linux-raid@vger.kernel.org Subject: Re: 5.1.21 Dell 2950 terrible swraid5 I/O performance with swraid on top of Perc 5/i raid0/jbod Message-ID: <20190819233709.76900bbf@natsu> In-Reply-To: <20190819070823.GH12521@merlins.org> References: <20190819070823.GH12521@merlins.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Mon, 19 Aug 2019 00:08:23 -0700 Marc MERLIN wrote: > > Default Cache Policy: WriteBack, ReadAheadNone, Direct, No Write Cache if Bad BBU > > Current Cache Policy: WriteBack, ReadAheadNone, Direct, No Write Cache if Bad BBU > > Default Access Policy: Read/Write > > Current Access Policy: Read/Write > > Disk Cache Policy : Disabled So does it have a BBU? (Battery backup unit) > I tried to disable the card's write cache to let linux and its 32GB of > RAM, do it better, but I didn't see a real improvement: I'd expect that on the contrary, you should look for ways to enable it, and force-enable even without that BBU (in case of lack of one), because it feels like what you did is disable disks' own write buffering, and not (only) the card's! What you are observing seems to me like what "dd" does with "oflag=dsync" (and comparable performance that it gets). Definitely feels like it's in some "extra safe mode" and, say, every 4KB piece of data leads to full flush to disk before accepting to write the next 4KB. More things to try, check if it's possible to set up disks not as 1-member RAID0, but 1-member "linear" ("JBOD"), or even 1-member RAID1, who knows maybe some of this would work better. -- With respect, Roman