From owner-freebsd-questions@FreeBSD.ORG Mon Apr 11 14:47:39 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 8F1081065670 for ; Mon, 11 Apr 2011 14:47:39 +0000 (UTC) (envelope-from DStaal@usa.net) Received: from mail.magehandbook.com (173-8-4-45-WashingtonDC.hfc.comcastbusiness.net [173.8.4.45]) by mx1.freebsd.org (Postfix) with ESMTP id 4922E8FC19 for ; Mon, 11 Apr 2011 14:47:37 +0000 (UTC) Received: from www.magehandbook.com (magehandbook.com [192.168.1.100]) by mail.magehandbook.com (Postfix) with ESMTP id EA99E29E9A for ; Mon, 11 Apr 2011 10:47:26 -0400 (EDT) Received: from 152.121.16.253 (SquirrelMail authenticated user daniel) by www.magehandbook.com with HTTP; Mon, 11 Apr 2011 10:47:27 -0400 Message-ID: In-Reply-To: <20110410063258.GA10022@dan.emsphone.com> References: <4DA131BD.3030805@telting.org> <20110410063258.GA10022@dan.emsphone.com> Date: Mon, 11 Apr 2011 10:47:27 -0400 From: "Daniel Staal" To: freebsd-questions@freebsd.org User-Agent: SquirrelMail/1.4.21 MIME-Version: 1.0 Content-Type: text/plain;charset=iso-8859-1 Content-Transfer-Encoding: 8bit X-Priority: 3 (Normal) Importance: Normal Subject: Re: ZFS Striping and Optimizing Capabilities X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: DStaal@usa.net List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 11 Apr 2011 14:47:39 -0000 On Sun, April 10, 2011 2:32 am, Dan Nelson wrote: > 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. One thought that hasn't been mentioned, and probably should be in this context: It depends a bit on how you add the disk. A disk can be added to a non-RAIDZ zpool as either a stripe or a mirror. If you add it as a mirror ('attach' in zpool terms), then yes it starts a background low priority process that copies data over. I don't really think that was your question, but it's closely enough related that I thought it might be relevant. In the context of stripes it probably isn't relevant. But it could be in the context of adding disks. Daniel T. Staal --------------------------------------------------------------- This email copyright the author. Unless otherwise noted, you are expressly allowed to retransmit, quote, or otherwise use the contents for non-commercial purposes. This copyright will expire 5 years after the author's death, or in 30 years, whichever is longer, unless such a period is in excess of local copyright law. ---------------------------------------------------------------