From owner-freebsd-fs@FreeBSD.ORG Sun Jan 22 08:11:17 2012 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 09F1D106564A for ; Sun, 22 Jan 2012 08:11:17 +0000 (UTC) (envelope-from peter.maloney@brockmann-consult.de) Received: from mo-p05-ob6.rzone.de (mo-p05-ob6.rzone.de [IPv6:2a01:238:20a:202:53f5::1]) by mx1.freebsd.org (Postfix) with ESMTP id 67A9A8FC08 for ; Sun, 22 Jan 2012 08:11:16 +0000 (UTC) X-RZG-AUTH: :LWIKdA2leu0bPbLmhzXgqn0MTG6qiKEwQRWfNxSw4HzYIwjsnvdDt2QV8d370WKsPpmd/9Y= X-RZG-CLASS-ID: mo05 Received: from [192.168.179.42] (hmbg-4d06fd87.pool.mediaWays.net [77.6.253.135]) by smtp.strato.de (cohen mo8) (RZmta 27.5 DYNA|AUTH) with (DHE-RSA-AES256-SHA encrypted) ESMTPA id f00d89o0M6AwAb for ; Sun, 22 Jan 2012 09:11:00 +0100 (MET) Message-ID: <4F1BC493.10304@brockmann-consult.de> Date: Sun, 22 Jan 2012 09:10:59 +0100 From: Peter Maloney User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:9.0) Gecko/20111222 Thunderbird/9.0.1 MIME-Version: 1.0 To: freebsd-fs@freebsd.org References: <4F193D90.9020703@digiware.nl> <20120121162906.0000518c@unknown> <4F1B0177.8080909@digiware.nl> <20120121230616.00006267@unknown> In-Reply-To: <20120121230616.00006267@unknown> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Subject: Re: Question about ZFS with log and cache on SSD with GPT X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 22 Jan 2012 08:11:17 -0000 Am 21.01.2012 23:06, schrieb Alexander Leidinger: >> Corsair reports: >> > Max Random 4k Write (using IOMeter 08): 50k IOPS (4k aligned) >> > So I guess that suggests 4k aligned is required. > Sounds like it is. > I'm not an SSD expert, but I read as much as I can, and found that many say that the sector size is not the only thing that matters on an SSD, but also the *erase boundary*. The size of the erase boundary varies, but 2MiB is a common factor (or 1MiB for 99% of them), so you can use that for all. The theory I read about is that when the SSD wants to write something, it must erase the whole erase block first. If it needs to erase a whole erase boundary space to write 512 bytes, that is just normal. But if you are misaligned, it often needs to erase 2 erase boundary spaces. Here is an example from our FreeBSD forum: http://forums.freebsd.org/showthread.php?t=19093 > I create the first partition at the usual 63 sectors offset from the > start of the disk (track 1) which is /unaligned/ with the SSD erase > block. The second partition is set to start at sector 21030912 > (10767826944 bytes) which is /aligned/ with the SSD erase block. > SSD erase block boundaries vary from manufacturer to manufacturer, but > a safe number to assume should be 1 MiB (1048576 bytes). In my testing, it made no difference. But as daniel mentioned: > With ZFS, the 'alignment' is on per-vdev -- therefore you will need to recreate the mirror vdevs again using gnop to make them 4k aligned. But I just resilvered to add my aligned disks and remove the old. If that applies to erase boundaries, then it might have hurt my test. Peter