From owner-freebsd-current@FreeBSD.ORG Fri Nov 15 16:15:09 2013 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 94B79603 for ; Fri, 15 Nov 2013 16:15:09 +0000 (UTC) Received: from mail-qc0-x22a.google.com (mail-qc0-x22a.google.com [IPv6:2607:f8b0:400d:c01::22a]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id 570E823F1 for ; Fri, 15 Nov 2013 16:15:09 +0000 (UTC) Received: by mail-qc0-f170.google.com with SMTP id n9so2271529qcw.1 for ; Fri, 15 Nov 2013 08:15:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; bh=MXnC7XgTkks5ty/M+WIxVPoKnS+K50EdOYdDUfHWK7k=; b=C8FgTYqVQ1B3aVcdV2/1JXjZcwJVMEsFZDncse83wfTGLG1vfxGBxpfFejReudAyF4 pul/pgw1hn/cWSRtldnrwr0gmAe2KgbirnJ5umKC70Vn/jlO75F6uTsT3Q4cIdUfg+m9 pGX1ewWTO5TjE3hOZU7/FudFxwqINn9UST6ui7vAdzBWF1Ls+JV6CxG7RmSDnuqUcNf7 7EWaIpQB6ZFllPlfoLELsQzo0+NIgnHs2o3P81t4NKyjcn0JizlyKPuF2Eoilha2x89n exYuuu2S7rH1M/mnQ5LLBu4b5WMdWSgLoFN0V7yMkAmYD8mlth7xYQ7+sDldxsAUL9Yu U1NA== MIME-Version: 1.0 X-Received: by 10.229.5.4 with SMTP id 4mr12086388qct.2.1384532108423; Fri, 15 Nov 2013 08:15:08 -0800 (PST) Received: by 10.96.180.233 with HTTP; Fri, 15 Nov 2013 08:15:08 -0800 (PST) In-Reply-To: <1384529791.7937.47924713.3321BFEF@webmail.messagingengine.com> 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> <1384529791.7937.47924713.3321BFEF@webmail.messagingengine.com> Date: Fri, 15 Nov 2013 18:15:08 +0200 Message-ID: Subject: Re: Defaults in 10.0 ZFS through bsdinstall From: Kimmo Paasiala To: FreeBSD current Content-Type: text/plain; charset=UTF-8 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 16:15:09 -0000 On Fri, Nov 15, 2013 at 5:36 PM, Mark Felder wrote: > > > 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. What I did on my system when I was still using ZFS was that I set atime off by default but enabled it explicitly on /var/mail and /home datasets. The thought was that it's needed for mailboxes in /var/mail and if I then decide to move the inboxes to user's home directories I won't get any surprises. Would that be a suitable compromise here? -Kimmo