From owner-freebsd-fs@FreeBSD.ORG Thu Jul 4 02:39:59 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 21C3C1D4 for ; Thu, 4 Jul 2013 02:39:59 +0000 (UTC) (envelope-from fjwcash@gmail.com) Received: from mail-qe0-x233.google.com (mail-qe0-x233.google.com [IPv6:2607:f8b0:400d:c02::233]) by mx1.freebsd.org (Postfix) with ESMTP id D75F31632 for ; Thu, 4 Jul 2013 02:39:58 +0000 (UTC) Received: by mail-qe0-f51.google.com with SMTP id a11so503262qen.38 for ; Wed, 03 Jul 2013 19:39:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=uZbTuagP+qZsykkVAkbkZQvoe/zVlDj0G3kofD4qZVs=; b=BFzSAmSVRtxnLCAZ06NVTaBQ9HFi4EWoyUpL6W//phvW+ZYSAZXGA/lTsqQvvGE2ZJ RqngaM/IUr+fLe9h5Kfn2MjOJ78PfYJ5Lhy2Lv6Cmz7o3G9rKUoLLrpwRIjryF8wgGWl TbGNPrJJN/xpxYP/IU51GLJeh5ey6TDxCE6+KPCV+7k25ZMYze7L1/pnW3bwaaf7Hd1A Ho2Of/f4WNRaE0GIw6BEAsSiXVaTypA9ZK/do6tMvK3MPZlEzRVtG5YOVVA0xGiEa2uj 2lBDdk6gq96TGTsKR4q+DTTbZ0H4R/+cTEG1l8OXuZ8hRqPBE81S+omac4gCIkLuH+yA uw5Q== MIME-Version: 1.0 X-Received: by 10.229.196.73 with SMTP id ef9mr961404qcb.85.1372905598427; Wed, 03 Jul 2013 19:39:58 -0700 (PDT) Received: by 10.49.49.135 with HTTP; Wed, 3 Jul 2013 19:39:58 -0700 (PDT) Received: by 10.49.49.135 with HTTP; Wed, 3 Jul 2013 19:39:58 -0700 (PDT) In-Reply-To: <20130704021535.GA77546@icarus.home.lan> References: <871u7g57rl.wl%berend@pobox.com> <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> Date: Wed, 3 Jul 2013 19:39:58 -0700 Message-ID: Subject: Re: EBS snapshot backups from a FreeBSD zfs file system: zpool freeze? From: Freddie Cash To: Jeremy Chadwick Content-Type: text/plain; charset=UTF-8 X-Content-Filtered-By: Mailman/MimeDel 2.1.14 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 02:39:59 -0000 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.