From owner-freebsd-questions@freebsd.org Fri Sep 16 21:18:40 2016 Return-Path: Delivered-To: freebsd-questions@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 2A11BBDDA77 for ; Fri, 16 Sep 2016 21:18:40 +0000 (UTC) (envelope-from brandon.wandersee@gmail.com) Received: from mail-it0-f42.google.com (mail-it0-f42.google.com [209.85.214.42]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 0263AD03; Fri, 16 Sep 2016 21:18:39 +0000 (UTC) (envelope-from brandon.wandersee@gmail.com) Received: by mail-it0-f42.google.com with SMTP id o3so25864986ita.1; Fri, 16 Sep 2016 14:18:39 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:references:user-agent:from:to:cc:subject :in-reply-to:date:message-id:mime-version; bh=fqdq+Ev4c0A/8UELFpTkhNgZ1nPw2TjQ3tyHhZgn7MM=; b=Im1ksz2jSgn+nLpIDqpbBVhdQXNZP3CB11XIHOyk1NTZ+8zsCp49gD5vCtMBw6ws+O 9ND6MsI3ejTgFBnvZh/m1SIWl0Yg1xIsk0212XbgS4fi7Dc/UvkDW80u0NStUAGshNMl WjQaNSFDB55hKJIAMmSDENvplxxzE0yJhqxnlKk2s4AySBQYassTuVsEzC8H7YeXFB+e Ny1TGwSaLfjXjN2pHnGc+MZsUlWeqEDUwvtSyxO+pftBrggiFCA7cFF32gsJx4ZwgoPR Whb+vXjMOpkC7546jP2Ue3NJYd/oM50ccJLeo0g65LdiMB1l41ZVEmRefNwaO8Ro2bZe +vQw== X-Gm-Message-State: AE9vXwOd+f1rriTahNe0OPFoKpTP3F7WKB5eEt/sIG7S3TvQOFc5GnEqzvJiW65bCtC4Vg== X-Received: by 10.36.111.199 with SMTP id x190mr8037075itb.61.1474060712741; Fri, 16 Sep 2016 14:18:32 -0700 (PDT) Received: from WorkBox.Home.gmail.com (97-116-17-17.mpls.qwest.net. [97.116.17.17]) by smtp.gmail.com with ESMTPSA id v7sm3651244ita.9.2016.09.16.14.18.31 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 16 Sep 2016 14:18:31 -0700 (PDT) References: <4bd29396-220a-e198-73b9-0de91b74d096@FreeBSD.org> User-agent: mu4e 0.9.16; emacs 24.5.1 From: Brandon J. Wandersee To: Matthew Seaman Cc: freebsd-questions@freebsd.org Subject: Re: 10.3 zpool/var canmount = off? In-reply-to: <4bd29396-220a-e198-73b9-0de91b74d096@FreeBSD.org> Date: Fri, 16 Sep 2016 16:18:31 -0500 Message-ID: <86d1k3tufs.fsf@WorkBox.Home> MIME-Version: 1.0 Content-Type: text/plain X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 16 Sep 2016 21:18:40 -0000 Matthew Seaman writes: > The point of having zroot/var (with canmount=off) that just acts as a > placeholder is so that eg. zroot/var/log or zroot/var/tmp (which you'll > see have 'canmount=on') get mounted in the right location in the file > system without becoming part of any boot environment. That means > there's only one copy of those filesystems and it always gets mounted > every time you reboot -- which is really what you want for eg. /var/log > but not correct for boot environments in general. Usually you'll have > several available, but only one of them should be mounted and active. Matthew covered all the big stuff, but the ability to create dataset trees with non-hierarchical mountpoints, or an unmounted dataset as the root of a dataset tree, is actually a very useful administration trick. Boot environments are one example, but it also lets you manage and easily roll back all parts of a system that are related to each other, but the files for which are stored in different parts of the filesystem. You could, for example, create a dataset tree for every component of an Apache or Nginx configuration. I have a tree of filesystems for everything related to ports/packages except distfiles, so I can roll everything back in lock-step if an upgrade goes bad while avoiding having to download everything again. -- :: Brandon J. Wandersee :: brandon.wandersee@gmail.com :: -------------------------------------------------- :: 'The best design is as little design as possible.' :: --- Dieter Rams ----------------------------------