From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BD7A4192D6B; Tue, 29 Jul 2025 22:24:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753827860; cv=none; b=P5KNPJObYPkuSmw7At2cLecv2Duzt4J5GIjdbJVYCxCgFardI7AaXmpw3SCVsM2ozswI1apYrBO1+a8YUIrQPwG1B036ses1ug4Nh1bNjlmALixMdqregFvWjhuDL1CnqNl7XCiTWrMVFplqFYTqkwStbOoeNhrNM7pubWPFZvg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753827860; c=relaxed/simple; bh=m+dW8qFaDNCO9oHehMLMxPVDKuVPYt5FuFimxhrAGkM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XP+U1CXIv59eVdLgoWmA4UurYVFxKclnCHB2kBIkofB7Lq34hfkNOAYed3GK3As1JsLQizbkOCf2zve7R+BJ/Lotve8OieUzkQhOeDGvvMQzTDqMCjFeq/FcmjwlADBNSZR1U7TBzT6nP50dF2+qXBt7GSblxXXtYBdWmrfNNjg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LCFt9qDx; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="LCFt9qDx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 89D95C4CEEF; Tue, 29 Jul 2025 22:24:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1753827860; bh=m+dW8qFaDNCO9oHehMLMxPVDKuVPYt5FuFimxhrAGkM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=LCFt9qDxsClSD68kzlnnlGhD+eOvATHtBbZccCr+h3+s0FQkyBnwNNShoYC7cBieT fk8FMnmfacFVzUTXfFYWln1EhZCNc83YAUuGpvxWOrinvokUD6VUIb3CydxnNsCFQ/ HirmFXPZp77xMYa7xBgRZQFbszVdRFY62G1c6XQ4RkVAuRhnSXntucoNqsZX3sY+NQ SA44QD6gFchobzO4+zcDETBb4a1qaiMzGCG+a5n3JUPg53CMiFnAhI3ddjRPdDXZS+ cF90ou9Bs72KQNCOtbqkxQ02sdrR8rUYiqKPgtYo7GtFS98arc4Caxeutj8o60L8za UgGZiQR5lPlag== Date: Tue, 29 Jul 2025 16:24:17 -0600 From: Keith Busch To: Hannes Reinecke Cc: Yu Kuai , Damien Le Moal , =?iso-8859-1?Q?Csord=E1s?= Hunor , Coly Li , hch@lst.de, linux-block@vger.kernel.org, "James E.J. Bottomley" , "Martin K. Petersen" , linux-scsi@vger.kernel.org, "yukuai (C)" Subject: Re: Improper io_opt setting for md raid5 Message-ID: References: <2b22f745-bbd5-4071-be9b-de9e4536f2d5@kernel.org> <6ab1be6e-380b-d4aa-dd71-f53373a66e29@huaweicloud.com> <655cb7e6-897a-4fab-a8ce-8832f2bc7274@kernel.org> <4767823c-2332-b3e1-67a6-2d7f55b48156@huaweicloud.com> <9c6f300a-f78f-de6e-4b99-453df377c7ba@huaweicloud.com> <9e85c424-6722-4315-b125-d0d26fc4574b@suse.de> Precedence: bulk X-Mailing-List: linux-scsi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9e85c424-6722-4315-b125-d0d26fc4574b@suse.de> On Tue, Jul 29, 2025 at 08:13:31AM +0200, Hannes Reinecke wrote: > > > Note that chunk_sectors limit is the *stripe* size, not per drive stride. > > > Beware of the wording here to avoid confusion (this is all already super > > > confusing !). > > > > This is something we're not in the same page :( For example, 8 disks > > raid5, with default chunk size. Then the above calculation is: > > > > 64k * 7 = 448k > > > > The chunksize I said is 64k... > > Hmm. I always thought that the 'chunksize' is the limit which I/O must > not cross to avoid being split. > So for RAID 4/5/6 I would have thought this to be the stride size, > as MD must split larger I/O onto two disks. > Sure, one could argue that the stripe size is the chunk size, but then > MD will have to split that I/O... Yah, I think that makes sense. At least the way nvme uses "chunk_size", it was assumed to mean the boundary for when the backend handling will split your request for different isolated media.