From owner-freebsd-hackers@FreeBSD.ORG Sun Jun 1 16:14:56 2014 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 25A0B776; Sun, 1 Jun 2014 16:14:56 +0000 (UTC) Received: from smtp1.multiplay.co.uk (smtp1.multiplay.co.uk [85.236.96.35]) by mx1.freebsd.org (Postfix) with ESMTP id B1ABF2950; Sun, 1 Jun 2014 16:14:55 +0000 (UTC) Received: by smtp1.multiplay.co.uk (Postfix, from userid 65534) id EA61F20E7088C; Sun, 1 Jun 2014 16:14:54 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.multiplay.co.uk X-Spam-Level: ** X-Spam-Status: No, score=2.0 required=8.0 tests=AWL,BAYES_00,DOS_OE_TO_MX, FSL_HELO_NON_FQDN_1,HELO_NO_DOMAIN,RDNS_DYNAMIC autolearn=no version=3.3.1 Received: from r2d2 (82-69-141-170.dsl.in-addr.zen.co.uk [82.69.141.170]) by smtp1.multiplay.co.uk (Postfix) with ESMTPS id 9FE4920E70886; Sun, 1 Jun 2014 16:14:50 +0000 (UTC) Message-ID: <8D276E03788643A39AABD6A7127B21A0@multiplay.co.uk> From: "Steven Hartland" To: "Nathan Whitehorn" , , References: <20140601004242.GA97224@bewilderbeast.blackhelicopters.org> <3D6974D83AE9495E890D9F3CA654FA94@multiplay.co.uk> <538B4CEF.2030801@freebsd.org> <1DB2D63312CE439A96B23EAADFA9436E@multiplay.co.uk> <538B4FD7.4090000@freebsd.org> Subject: Re: fdisk(8) vs gpart(8), and gnop Date: Sun, 1 Jun 2014 17:14:54 +0100 MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=response Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5931 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.6157 X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 01 Jun 2014 16:14:56 -0000 ----- Original Message ----- From: "Nathan Whitehorn" To: "Steven Hartland" ; ; Sent: Sunday, June 01, 2014 5:07 PM Subject: Re: fdisk(8) vs gpart(8), and gnop > On 06/01/14 09:00, Steven Hartland wrote: >> >> ----- Original Message ----- From: "Nathan Whitehorn" >> >> To: ; >> Sent: Sunday, June 01, 2014 4:55 PM >> Subject: Re: fdisk(8) vs gpart(8), and gnop >> >> >>> On 06/01/14 08:52, Steven Hartland wrote: >>>> ----- Original Message ----- From: "Mark Felder" >>>> >>>>> On May 31, 2014, at 20:57, Freddie Cash wrote: >>>>> >>>>>> There's a sysctl where you can set the minimum ashift for zfs. >>>>>> Then you >>>>>> never need to use gnop. >>>>>> >>>>>> I believe it's part of 10.0? >>>>> >>>>> I've not seen this yet. What we need is to port the ability to set >>>>> ashift at pool creation time: >>>>> >>>>> $ zpool create -o ashift=12 tank mirror disk1 disk2 mirror disk3 disk4 >>>>> >>>>> I believe the Linux zfs port has this functionality now, but we >>>>> still do not. >>>> >>>> We don't have that direct option yet but you can achieve the >>>> same thing by setting: vfs.zfs.min_auto_ashift=12 >>>> >>> Does anyone have any objections to me changing this default, right >>> now, today? >>> -Nathan >> >> I think you will get some objections to that, as it can have quite an >> impact >> on the performance for disks which are 512, due to the increased >> overhead of >> transfering 4k when only 512 is really required. This has a more dramatic >> impact on RAIDZx due too. >> >> Personally we run a custom kernel on our machines which has just this >> change >> in it to ensure capability with future disks, so I can confirm it does >> indeed >> have the desired effect :) > > So the discussion here is related to what to do about the installer. The > current ZFS component unconditionally creates gnops all over the place > to set ashift to 4k. That's across the board worse: it has exactly the > performance impact of changing the default of this sysctl (whatever that > is), it can't easily be overridden (which the sysctl can), and it's a > horrible hack to boot. There are a few options: > > 1. Change the default of vfs.zfs.min_auto_ashift > 2. Have the same effect but in a vastly worse way by adjusting the > installer to create gnops > 3. Have ZFS choose by itself and decide to do that permanently. > > Our ATA code is good about reporting block sizes now, so (3) isn't a big > issue except for the mixed-pool case, which is a huge PITA. > > We need to choose one of these. I favor (1). I wasn't aware of that but it should do #3 min_auto_ashift is a bigger discussion. Regards Steve