From owner-freebsd-fs@FreeBSD.ORG Thu Jul 4 02:51:16 2013 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) by hub.freebsd.org (Postfix) with ESMTP id 07D675B6 for ; Thu, 4 Jul 2013 02:51:16 +0000 (UTC) (envelope-from jdc@koitsu.org) Received: from relay3-d.mail.gandi.net (relay3-d.mail.gandi.net [217.70.183.195]) by mx1.freebsd.org (Postfix) with ESMTP id B92CE169B for ; Thu, 4 Jul 2013 02:51:15 +0000 (UTC) Received: from mfilter3-d.gandi.net (mfilter3-d.gandi.net [217.70.178.133]) by relay3-d.mail.gandi.net (Postfix) with ESMTP id B01C6A80CA; Thu, 4 Jul 2013 04:51:04 +0200 (CEST) X-Virus-Scanned: Debian amavisd-new at mfilter3-d.gandi.net Received: from relay3-d.mail.gandi.net ([217.70.183.195]) by mfilter3-d.gandi.net (mfilter3-d.gandi.net [10.0.15.180]) (amavisd-new, port 10024) with ESMTP id 9vMLkqfAvCKQ; Thu, 4 Jul 2013 04:51:03 +0200 (CEST) X-Originating-IP: 76.102.14.35 Received: from jdc.koitsu.org (c-76-102-14-35.hsd1.ca.comcast.net [76.102.14.35]) (Authenticated sender: jdc@koitsu.org) by relay3-d.mail.gandi.net (Postfix) with ESMTPSA id D3659A80C7; Thu, 4 Jul 2013 04:51:02 +0200 (CEST) Received: by icarus.home.lan (Postfix, from userid 1000) id 0220373A1E; Wed, 3 Jul 2013 19:51:01 -0700 (PDT) Date: Wed, 3 Jul 2013 19:51:00 -0700 From: Jeremy Chadwick To: Freddie Cash Subject: Re: EBS snapshot backups from a FreeBSD zfs file system: zpool freeze? Message-ID: <20130704025100.GB78374@icarus.home.lan> References: <87mwq34emp.wl%berend@pobox.com> <20130703200241.GB60515@in-addr.com> <87k3l748gb.wl%berend@pobox.com> <20130703233631.GA74698@icarus.home.lan> <87d2qz42q4.wl%berend@pobox.com> <20130704010815.GB75529@icarus.home.lan> <8761wr3xxk.wl%berend@pobox.com> <20130704021535.GA77546@icarus.home.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Cc: FreeBSD Filesystems X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 04 Jul 2013 02:51:16 -0000 On Wed, Jul 03, 2013 at 07:39:58PM -0700, Freddie Cash wrote: > On 2013-07-03 7:16 PM, "Jeremy Chadwick" wrote: > > > > On Thu, Jul 04, 2013 at 01:40:07PM +1200, Berend de Boer wrote: > > > >>>>> "Jeremy" == Jeremy Chadwick writes: > > > > > > > > > Jeremy> Also, because nobody seems to warn others of this: if > > > Jeremy> you go the ZFS route on FreeBSD, please do not use > > > Jeremy> features like dedup or compression. > > > > > > Exactly the two reasons why I'm experimenting with FreeBSD on AWs. > > > > > > Please tell me more. > > > > dedup has immense and crazy memory requirements; the commonly referenced > > model (which is in no way precise, it's just a general recommendation) > > is that for every 1TB of data you need 1GB of RAM just for the DDT > > (deduplication table)) -- understand that ZFS's ARC also eats lots of > > memory, so when I say 1GB of RAM, I'm talking about that being *purely > > dedicated* to DDT. > > Correction: 1 GB of *ARC* space per TB of *unique* data in the pool. Each > unique block in the pool gets an entry in the DDT. > > You can use L2ARC to store the DDT, although it takes ARC space to track > data in L2ARC, so you can't go crazy (512 GB L2 with only 16 GB ARC is a > no-no). > > However, you do need a lot of RAM to make dedupe work, and your I/O does > drop through the floor. Thanks Freddie -- I didn't know this (re: ARC space per TB of unique data); wasn't aware that's where the DDT got placed. (Actually makes sense now that I think about it...) -- | Jeremy Chadwick jdc@koitsu.org | | UNIX Systems Administrator http://jdc.koitsu.org/ | | Making life hard for others since 1977. PGP 4BD6C0CB |