From owner-freebsd-fs@FreeBSD.ORG Mon Nov 7 19:35:51 2011 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 6DC6C1065677 for ; Mon, 7 Nov 2011 19:35:51 +0000 (UTC) (envelope-from freebsd-fs@m.gmane.org) Received: from lo.gmane.org (lo.gmane.org [80.91.229.12]) by mx1.freebsd.org (Postfix) with ESMTP id F0EDE8FC0C for ; Mon, 7 Nov 2011 19:35:50 +0000 (UTC) Received: from list by lo.gmane.org with local (Exim 4.69) (envelope-from ) id 1RNUyx-0000Zf-4Q for freebsd-fs@freebsd.org; Mon, 07 Nov 2011 20:35:47 +0100 Received: from ib-jtotz.ib.ic.ac.uk ([155.198.110.220]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Mon, 07 Nov 2011 20:35:47 +0100 Received: from jtotz by ib-jtotz.ib.ic.ac.uk with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Mon, 07 Nov 2011 20:35:47 +0100 X-Injected-Via-Gmane: http://gmane.org/ To: freebsd-fs@freebsd.org From: Johannes Totz Date: Mon, 07 Nov 2011 19:35:34 +0000 Lines: 41 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Complaints-To: usenet@dough.gmane.org X-Gmane-NNTP-Posting-Host: ib-jtotz.ib.ic.ac.uk User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:7.0.1) Gecko/20110929 Thunderbird/7.0.1 In-Reply-To: Subject: Re: ZFS question - clones vs dedupe 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, 07 Nov 2011 19:35:51 -0000 On 31/10/2011 10:34, Ivan Natchkov wrote: > Hello to everyone, > > I have the following situation. EVA 4000 with 3T disk space and one > oracle DB 1,2T on a different storage. On our EVA we must keep copy of > this DB with non stop applying of archive logs. In addition we need > 3-4 development DB's plus 3-4 test DB's which are copies of the > original 1,2T DB and are stored on the EVA. We are thinking about 2 > scenarios. 1) 8 clonings with keeping differences between the clonings > 2) to have 8 different DB made with zfs send/receive on the same > storage with deduplication switch ON. > > In both scenario we want the DB with applying logs to be with dedupe > switched off because of the performance issues. > > I have 20 Gigs of RAM and the DDT table is possible to be kept in it > with some tuning of sysctl. > > Which scenario would you recommend in terms of performance? I don't understand your requirement, so cannot give a recommendation. However, I've been playing with dedup for the past few weeks and so far I have mixed feelings about it. There are some stability issues (zfs bits keeps live-locking sometimes) and write-performance kinda sucks. Especially deleting larger sets of data (like snapshots or big files) takes ages, up to a point that makes SSH logins take a few minutes. Also, after a crash it takes very long to boot up again, maybe because it's rolling back some transactions or something... I have about 1.5 TB of data, dedup ratio is around 1.7. The machine only has 6 GB of RAM, and I've increased the metadata limit to 4 GB. However, I log actual arc-size periodically and very often it's nowhere near its limit... Oh yeah, and there's lzjb compression as well. This prob adds a bit of trouble, see compression thread from a few weeks ago. Johannes