From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lists.gentoo.org (pigeon.gentoo.org [208.92.234.80]) by finch.gentoo.org (Postfix) with ESMTP id 98215138010 for ; Sun, 26 Aug 2012 11:43:37 +0000 (UTC) Received: from pigeon.gentoo.org (localhost [127.0.0.1]) by pigeon.gentoo.org (Postfix) with SMTP id 4FA17E0453; Sun, 26 Aug 2012 11:43:15 +0000 (UTC) Received: from mx.virtyou.com (mx.virtyou.com [178.33.32.244]) by pigeon.gentoo.org (Postfix) with ESMTP id 6971CE04EC for ; Sun, 26 Aug 2012 11:41:10 +0000 (UTC) Received: from [127.0.0.1] (xdsl-78-35-154-213.netcologne.de [78.35.154.213]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by mx.virtyou.com (Postfix) with ESMTPSA id 6B41EDC04E for ; Sun, 26 Aug 2012 13:41:09 +0200 (CEST) Message-ID: <503A0B55.3030206@wonkology.org> Date: Sun, 26 Aug 2012 13:41:09 +0200 From: Alex Schuster Organization: Wonkology User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:14.0) Gecko/20120713 Thunderbird/14.0 Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-Id: Gentoo Linux mail X-BeenThere: gentoo-user@lists.gentoo.org Reply-to: gentoo-user@lists.gentoo.org MIME-Version: 1.0 To: gentoo-user@lists.gentoo.org Subject: Re: [gentoo-user] SSD performance tweaking References: <503602B8.3050507@wonkology.org> <20120824092548.GA13922@eisen.lan> In-Reply-To: <20120824092548.GA13922@eisen.lan> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Archives-Salt: e3d299ca-f55e-4868-b637-08e7fc4faaac X-Archives-Hash: a4d9df095c82f5b533c05a7a1700f350 Frank Steinmetzger writes: > On Thu, Aug 23, 2012 at 12:15:20PM +0200, Alex Schuster wrote: >> The size of an erasable block of SSDs is even larger, usually 512K, it >> would be best to align to that, too. A partition offset of 512K or 1M >> would avoid this. > > Unless the filesystem knows this and starts bigger files at those 512 k > boundaries (so really only one erase cycle is needed for files <=512 k), > isn't this fairly superfluous? Yes, I think it is. When you search for SSD alignment, you read about this alignment all the time, even on the German Wikipedia, and many resources say that this can have a big impact on performance. But I could not find a real explanation at all. Besides that, it's not so easy to do the alignment, at least when using LVM. I read that LVM adds 192K header information, so even if you align the partition start to an erasable block size of 512K, the actual content is not aligned. See [*] for information how to overcome this. That is, if you believe the alignment to erasable blocks is important, personally I do not know what to think now. It wouldn't hurt, so why not apply it, but it seems like snake oil to me now. Wonko http://tytso.livejournal.com/2009/02/20/