From owner-freebsd-questions@FreeBSD.ORG Sun Apr 10 06:33:00 2011 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 200E21065670 for ; Sun, 10 Apr 2011 06:33:00 +0000 (UTC) (envelope-from dan@dan.emsphone.com) Received: from email2.allantgroup.com (email2.emsphone.com [199.67.51.116]) by mx1.freebsd.org (Postfix) with ESMTP id D5EEF8FC12 for ; Sun, 10 Apr 2011 06:32:59 +0000 (UTC) Received: from dan.emsphone.com (dan.emsphone.com [199.67.51.101]) by email2.allantgroup.com (8.14.4/8.14.4) with ESMTP id p3A6WwJF063022 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Sun, 10 Apr 2011 01:32:58 -0500 (CDT) (envelope-from dan@dan.emsphone.com) Received: from dan.emsphone.com (smmsp@localhost [127.0.0.1]) by dan.emsphone.com (8.14.4/8.14.4) with ESMTP id p3A6Ww3h004693 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Sun, 10 Apr 2011 01:32:58 -0500 (CDT) (envelope-from dan@dan.emsphone.com) Received: (from dan@localhost) by dan.emsphone.com (8.14.4/8.14.4/Submit) id p3A6Ww0D004692; Sun, 10 Apr 2011 01:32:58 -0500 (CDT) (envelope-from dan) Date: Sun, 10 Apr 2011 01:32:58 -0500 From: Dan Nelson To: Chris Telting Message-ID: <20110410063258.GA10022@dan.emsphone.com> References: <4DA131BD.3030805@telting.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4DA131BD.3030805@telting.org> X-OS: FreeBSD 8.2-PRERELEASE User-Agent: Mutt/1.5.21 (2010-09-15) X-Virus-Scanned: clamav-milter 0.97 at email2.allantgroup.com X-Virus-Status: Clean X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.6 (email2.allantgroup.com [199.67.51.78]); Sun, 10 Apr 2011 01:32:58 -0500 (CDT) X-Scanned-By: MIMEDefang 2.68 on 199.67.51.78 Cc: freebsd-questions@freebsd.org Subject: Re: ZFS Striping and Optimizing Capabilities X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 10 Apr 2011 06:33:00 -0000 In the last episode (Apr 09), Chris Telting said: > Just a few questions about what ZFS actually does. So if anyone has > intimate knowledge about ZFS's implementation on Freebsd I'm sure I and > others would appreciate the answers. > > When you add a second and or thrid drive/partition to a zpool I'm assuming > that it's going to start using the drives like a raid 0 stripe. How do > the ZFS versions differ in this? Does it immediately start striping all > files in the background on low priority or does it do it as files are > accessed? Does ZFS in any way do performance testing of Currently ZFS never moves a block once it has been written. The whole implementation of copy-on-write and snapshots relies on this. If you add a new zvol to a pool, new data will get balanced across all the zvols but old data will stay where it was. Ideally you should expand pools before they get too full, or zpool export/import them into new pools if you want good distribution over all disks. There have been hints for the last few years of a "bp rewite" feature appearing, but it has never materialized. -- Dan Nelson dnelson@allantgroup.com