From owner-freebsd-doc@FreeBSD.ORG Sun Jan 8 00:14:58 2012 Return-Path: Delivered-To: doc@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 1AA9F10657AC for ; Sun, 8 Jan 2012 00:14:58 +0000 (UTC) (envelope-from amvandemore@gmail.com) Received: from mail-we0-f182.google.com (mail-we0-f182.google.com [74.125.82.182]) by mx1.freebsd.org (Postfix) with ESMTP id A488F8FC16 for ; Sun, 8 Jan 2012 00:14:57 +0000 (UTC) Received: by werb13 with SMTP id b13so2820223wer.13 for ; Sat, 07 Jan 2012 16:14:56 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=NsvIKzrJTG0cPD2WyJywE7N8FQBpHhALw0g4M9lGzGI=; b=ascSwAUBiwV8NzvORx4sHHThZU2PGWXKDm5AsbMOKu0lSwz9R/HEYrJrkZjMa991Yp vBjcrGPtItr3hPQOjhWM1PoiBnuZvLWlMrZOIOwhH1CxClzCftWvVMN5gGR7iIFF+feu uUnG8TLo4+surfz3vjUNntyRZDIiL6cAQvjio= MIME-Version: 1.0 Received: by 10.216.136.234 with SMTP id w84mr1306091wei.9.1325981696722; Sat, 07 Jan 2012 16:14:56 -0800 (PST) Received: by 10.223.157.198 with HTTP; Sat, 7 Jan 2012 16:14:56 -0800 (PST) In-Reply-To: References: Date: Sat, 7 Jan 2012 18:14:56 -0600 Message-ID: From: Adam Vande More To: Benjamin Kaduk Content-Type: text/plain; charset=ISO-8859-1 X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Cc: doc@freebsd.org Subject: Re: Suggestion for Handbook X-BeenThere: freebsd-doc@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Documentation project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 08 Jan 2012 00:14:58 -0000 On Fri, Jan 6, 2012 at 11:17 PM, Benjamin Kaduk wrote: > I think dd would be preferred precisely because it does not use sparse > files -- all blocks for the image will be allocated. > > If a sparse file was used, and the physical disk became close to full, > then when the system goes to make a write to the image and the backing file > cannot be grown, things are unlikely to fail gracefully. > A full image imposes other penalties and drawbacks. If you use a modern hypervisor, it's default backing store will be some type of glorified sparse file(vmdk, vdi, qcow2 -- at least AFAIK on qcow2). I would venture to guess that is because those communities are aware of the advantages and disadvantages of each with sparse files chosen consistently as the default. Furthermore, this is the error you get when writing to an overcommited sparse file: No space left on device galacticdominator# diskinfo /dev/md0 /dev/md0 512 1073741824000 2097152000 0 0 galacticdominator# diskinfo /dev/zvol/zoot/usr/home/zvol-test /dev/zvol/zoot/usr/home/zvol-test 512 5242880 10240 0 0 So it seems a sysadmin ought to be able to deal with that. -- Adam Vande More