From owner-freebsd-questions@freebsd.org Mon Jun 13 00:55:05 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 3E5E7AF1BC8 for ; Mon, 13 Jun 2016 00:55:05 +0000 (UTC) (envelope-from brandon.wandersee@gmail.com) Received: from mail-it0-f43.google.com (mail-it0-f43.google.com [209.85.214.43]) (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 1713F2B63 for ; Mon, 13 Jun 2016 00:55:04 +0000 (UTC) (envelope-from brandon.wandersee@gmail.com) Received: by mail-it0-f43.google.com with SMTP id z189so37301717itg.0 for ; Sun, 12 Jun 2016 17:55:04 -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=TqxwgYEvk2KZuzeDp8s+rO68IQTNb1zA7XU73/8E2pc=; b=RmgZYsQ8CC9p1J/97yqANQcjjPd+lFBQe2l27vDHa4n1akWyMXhJW564qwIPYRSxT2 XSKjiNr5eHuqCYzLJ9YmmLvHDsc+hGjd5SeDd+2P8JRtkhAQ/IOdfcArl1Zlt0etgQF6 6AnqUaOUwbncrS5CtnwOUztPUFtnX6AYMAVt7EIq3AdgiyGzSIlnH8FAAJAMTvzrM78T JuYt0xbUHdo8JxETZRKAsB9su9/uN2vptIeYbCSySHr75rFt+VvLAmIzLo7+Nzs3henl +xgIG9GZhGgIk1Zzh6rd+UeJSvarX62KcT5baYW8H0ln7QBWGX5aM4VdbzdsQ/dYsTcx Gb4w== X-Gm-Message-State: ALyK8tLzuLBKx3Lomq/XJMrrPwKMawR9kSZDTlnVCNzaUpZmZrLZ1AzvBqIhB3IB2ebb0A== X-Received: by 10.36.60.20 with SMTP id m20mr14011970ita.81.1465778836583; Sun, 12 Jun 2016 17:47:16 -0700 (PDT) Received: from WorkBox.Home.gmail.com (174-30-251-248.mpls.qwest.net. [174.30.251.248]) by smtp.gmail.com with ESMTPSA id h193sm4190683ioe.40.2016.06.12.17.47.15 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 12 Jun 2016 17:47:15 -0700 (PDT) References: <86shwiax38.fsf@WorkBox.Home> <22e9b8aa-3171-f399-f3a8-b71eb92210f5@rawbw.com> User-agent: mu4e 0.9.16; emacs 24.5.1 From: Brandon J. Wandersee To: Yuri Cc: FreeBSD Questions Subject: Re: ZFS: Is 'zpool add' really irreversible? In-reply-to: <22e9b8aa-3171-f399-f3a8-b71eb92210f5@rawbw.com> Date: Sun, 12 Jun 2016 19:47:17 -0500 Message-ID: <864m8xewyy.fsf@WorkBox.Home> MIME-Version: 1.0 Content-Type: text/plain X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 13 Jun 2016 00:55:05 -0000 Yuri writes: > People may reasonably want to remove some disks in some layouts, due > to failures, etc, and ZFS just lacks the flexibility to do that. Obviously, if you're dealing with any sort of RAID you'll occasionally be replacing failed disks; ZFS is no different, and you can swap out disks while the system is running. You just can't remove a *virtual device*. You can't just shuffle disks around willy-nilly, because you'd effectively destroy the storage pool in the process. There's a minimum number of disks that need to be attached, and that minimum changes as you add virtual (not necessarily physical) devices to a pool. Traditional RAID has the same sort of limitation: create a RAID 5 array out of three disks, then remove two disks. You've just destroyed the array. If you want to temporarily add a single disk to a system, you can just create a second pool on it. There's no arbitrary limit to how many pools a system can have. ZFS has real limitations, but they're not that strict. -- :: Brandon J. Wandersee :: brandon.wandersee@gmail.com :: -------------------------------------------------- :: 'The best design is as little design as possible.' :: --- Dieter Rams ----------------------------------