From owner-freebsd-fs@FreeBSD.ORG Mon Aug 13 20:53:24 2012 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 4EB79106566C for ; Mon, 13 Aug 2012 20:53:24 +0000 (UTC) (envelope-from prvs=15723815ec=killing@multiplay.co.uk) Received: from mail1.multiplay.co.uk (mail1.multiplay.co.uk [85.236.96.23]) by mx1.freebsd.org (Postfix) with ESMTP id C9F298FC14 for ; Mon, 13 Aug 2012 20:53:23 +0000 (UTC) X-Spam-Processed: mail1.multiplay.co.uk, Mon, 13 Aug 2012 21:53:00 +0100 X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on mail1.multiplay.co.uk X-Spam-Level: X-Spam-Status: No, score=-5.0 required=6.0 tests=USER_IN_WHITELIST shortcircuit=ham autolearn=disabled version=3.2.5 Received: from r2d2 ([188.220.16.49]) by mail1.multiplay.co.uk (mail1.multiplay.co.uk [85.236.96.23]) (MDaemon PRO v10.0.4) with ESMTP id md50021220368.msg for ; Mon, 13 Aug 2012 21:52:59 +0100 X-MDRemoteIP: 188.220.16.49 X-Return-Path: prvs=15723815ec=killing@multiplay.co.uk X-Envelope-From: killing@multiplay.co.uk X-MDaemon-Deliver-To: freebsd-fs@freebsd.org Message-ID: From: "Steven Hartland" To: "Olivier Smedts" , "Steven Schlansker" References: <7BDA02A3-99ED-4F67-9B2D-5AAF1523642E@helenius.fi> Date: Mon, 13 Aug 2012 21:52:43 +0100 MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5931 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.6157 Cc: freebsd-fs@freebsd.org, Petri Helenius Subject: Re: zero deleted blocks X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 13 Aug 2012 20:53:24 -0000 ----- Original Message ----- From: "Olivier Smedts" > 2012/8/13 Steven Schlansker : >> >> On Aug 13, 2012, at 2:27 AM, Olivier Smedts wrote: >>> Did you try a classic "dd if=/dev/zero of=a-file-on-the-pool" ? This >>> won't give good results if you do this on a filesystem with >>> compression enabled. >> >> ZFS uses copy on write (http://en.wikipedia.org/wiki/ZFS#Copy-on-write_transactional_model) so overwriting with zeroes will >> actually allocate new space to hold all the zeroed data and leave the old data mostly untouched. > > Only until all the free space is consumed ! Also need to ensure compression isnt turned on and its not an device that does compression on disk / disk controller such as Sandforce based SSD's as that could resulting in something other than the intended behavour. ================================================ This e.mail is private and confidential between Multiplay (UK) Ltd. and the person or entity to whom it is addressed. In the event of misdirection, the recipient is prohibited from using, copying, printing or otherwise disseminating it or any information contained in it. In the event of misdirection, illegible or incomplete transmission please telephone +44 845 868 1337 or return the E.mail to postmaster@multiplay.co.uk.