From owner-freebsd-current@FreeBSD.ORG Fri Nov 15 15:36:34 2013 Return-Path: Delivered-To: freebsd-current@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 639D32B9 for ; Fri, 15 Nov 2013 15:36:34 +0000 (UTC) Received: from out3-smtp.messagingengine.com (out3-smtp.messagingengine.com [66.111.4.27]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id 381CC213E for ; Fri, 15 Nov 2013 15:36:33 +0000 (UTC) Received: from compute5.internal (compute5.nyi.mail.srv.osa [10.202.2.45]) by gateway1.nyi.mail.srv.osa (Postfix) with ESMTP id 7AEC02089D for ; Fri, 15 Nov 2013 10:36:31 -0500 (EST) Received: from web3 ([10.202.2.213]) by compute5.internal (MEProxy); Fri, 15 Nov 2013 10:36:31 -0500 DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; d= messagingengine.com; h=message-id:from:to:mime-version :content-transfer-encoding:content-type:in-reply-to:references :subject:date; s=smtpout; bh=8Cs43nWT3ZzFaNnCb6WaySliAAg=; b=prk M9g51hSsMu4mgJw2M/mBJzJpsGtjHcTtomq1QUyN3gzY8cvZXJjrrssgS1jID50U d11nNj7btjaCs89NZF7mf+5GV6IIg5Q4PbTQQrpDwegUre1eNnvDFbgSINlZORh6 ICZSp12d2jKfqRWX90ki6cl/TZnYALO6vQGZHlQI= Received: by web3.nyi.mail.srv.osa (Postfix, from userid 99) id 5A7FB103A66; Fri, 15 Nov 2013 10:36:31 -0500 (EST) Message-Id: <1384529791.7937.47924713.3321BFEF@webmail.messagingengine.com> X-Sasl-Enc: 7M4Me4UeU7kzOBKjub1IeC1aMOlmzIGWtZzTjZH0QkaX 1384529791 From: Mark Felder To: freebsd-current@freebsd.org MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain X-Mailer: MessagingEngine.com Webmail Interface - ajax-d4893488 In-Reply-To: <5285E827.1090501@freebsd.org> References: <20131114173423.GA21761@blazingdot.com> <59A9B68B-4134-4217-83F3-B99759174EFE@fisglobal.com> <5285148E.6020903@allanjude.com> <3D3332FA-0ABF-4573-8E65-4E7FBB37100B@fisglobal.com> <1384462198.13183.47596065.6F8E7BCD@webmail.messagingengine.com> <55232624-3B76-4781-91E0-0C2A6260144D@fisglobal.com> <5285E827.1090501@freebsd.org> Subject: Re: Defaults in 10.0 ZFS through bsdinstall Date: Fri, 15 Nov 2013 09:36:31 -0600 X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.16 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 15 Nov 2013 15:36:34 -0000 On Fri, Nov 15, 2013, at 3:23, Stefan Esser wrote: > Am 14.11.2013 22:02, schrieb Teske, Devin: > > On Nov 14, 2013, at 12:49 PM, Mark Felder wrote: > >> We don't even do installs on UFS with atime disabled by default in fstab > >> so why should we so suddenly change course for ZFS? > >> > > > > You've made a good point. > > There is major difference between UFS and ZFS: UFS allows in-place > updates of i-node fields (like atime), while ZFS uses COW for all > data, file contents and meta-data like the i-nodes. > > With atime ON on UFS you'll see a small number of writes on > file-systems that are only read - we are used to accept that. > > On ZFS every update of atime causes a write of the meta-data to > a free location on disk, then updates of all data structures > that reference that meta-data up to the root of the tree (the > uberblock). An update of a few bytes turns out to write tens > of KB for each atime update (within the TXG sync interval, which > defaults to 5 seconds on FreeBSD). If you create snapshots, then > each snapshot will contain a copy of the metadata that was valid > at the time of the snapshot (well, that's not so different from > the situation with UFS snapshots, just that the data structures > are much more complex and larger in the ZFS case). Due to the > ease and speed of snapshot creation with ZFS there probably are > a magnitude or more snapshots on a typical ZFS system than on > one using UFS (I currently have a few hundred and have turned off > periodic snapshot generation on many unimportant file-systems, > already). > > I really hope that we get relatime (with minor variations that > were discussed a few months ago) and that we make it the default > in some future release ... > Thanks for this in-depth explanation. I wasn't aware that atime was quite so expensive on ZFS.