From owner-freebsd-questions@FreeBSD.ORG Mon May 13 12:40:58 2013 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.FreeBSD.org [8.8.178.115]) by hub.freebsd.org (Postfix) with ESMTP id 4793811A for ; Mon, 13 May 2013 12:40:58 +0000 (UTC) (envelope-from paul@kraus-haus.org) Received: from mail-vb0-x22e.google.com (mail-vb0-x22e.google.com [IPv6:2607:f8b0:400c:c02::22e]) by mx1.freebsd.org (Postfix) with ESMTP id 0910DF60 for ; Mon, 13 May 2013 12:40:57 +0000 (UTC) Received: by mail-vb0-f46.google.com with SMTP id 10so5091853vbe.5 for ; Mon, 13 May 2013 05:40:57 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=x-received:subject:mime-version:content-type:from:in-reply-to:date :cc:content-transfer-encoding:message-id:references:to:x-mailer :x-gm-message-state; bh=yiHDrODK4yqhUpHEmPfn98ofr4y6wISjDvTiePSTHME=; b=jefLUYtqNMCkwIyL5KGr4pgydYOimZ3PGWboLxvY/sAveI2/Wq8kV60Z44eCGC1oQC 0m26HVzdBt4pkuuv4vwX5dvrypk2YHk+o+ElSAiT610/tFxtRKM3eHWevk10NDkDdSwQ aKENUwCl/msbFkkc4KHmBo+Arb7qTL7SIm02eNLLsofekxxtRdXgSsfja3QMS/yVteiG qHxj+fFGq/Ry7n2a1tASUE6goowBW+WBUkY/+/2J5FZVvrvfPOf5YZ4bz/8DDRFgAehd zAYo7KfDaiyCnYpkDqC5Ev6a5o7EJ/2rtI6RANvi28jVACw4bbDW+6HSIBcNHrhu7TzK Lquw== X-Received: by 10.58.54.101 with SMTP id i5mr18316046vep.43.1368448857284; Mon, 13 May 2013 05:40:57 -0700 (PDT) Received: from [192.168.2.66] ([96.236.21.119]) by mx.google.com with ESMTPSA id y20sm12985260vds.7.2013.05.13.05.40.56 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 13 May 2013 05:40:56 -0700 (PDT) Subject: Re: ZFS mirror install /mnt is empty Mime-Version: 1.0 (Mac OS X Mail 6.3 \(1503\)) Content-Type: text/plain; charset=windows-1252 From: Paul Kraus In-Reply-To: Date: Mon, 13 May 2013 08:40:55 -0400 Content-Transfer-Encoding: quoted-printable Message-Id: <472E17AF-B249-4FD3-8F5E-716F8B7867F5@kraus-haus.org> References: <5190058D.2030705@micite.net> To: =?windows-1252?Q?Trond_Endrest=F8l?= X-Mailer: Apple Mail (2.1503) X-Gm-Message-State: ALoCoQkBiUghnyqQ7nH5DLvDVQ4kAxLLjiYnilSg5nT/u2+7O0laLWBDFn2wgX25S1YDR09K8oiV Cc: "freebsd-questions@freebsd.org List" X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 13 May 2013 12:40:58 -0000 On May 13, 2013, at 1:58 AM, Trond Endrest=F8l = wrote: > Due to advances in hard drive technology, for the worse I'm afraid,=20 > i.e. 4K disk blocks, I wouldn't bother enabling compression on any ZFS=20= > file systems. I might change my blog posts to reflect this stop gap. >=20 > If you do happen to have 4K drives, you might want to check out this=20= > blog post: >=20 > = https://ximalas.info/2012/01/11/new-server-and-first-attempt-at-running-fr= eebsdamd64-with-zfs-for-all-storage/ I did look, it doesn't explain why not to enable compression on = 4k sector drives. =46rom discussion on the zfs-discuss lists (both the old one = from OpenSolaris and the new one at Illumos) the only issue with 4K = sector drives is mixing 0.5K sector and 4K sector drives. You can tunes = the zpool offset to handle 4K sector drives just fine, but it is a pool = wide tuning. http://zfsday.com/wp-content/uploads/2012/08/Why-4k_.pdf has = some 4K background, and the only mention I see of compression and 4K is = that you may get less. But=85 you really need to test your data to see = if turning compression on is beneficial with any dataset. There is = noticeable computational overhead to enabling compression. If you are = CPU bound, then you will get better performance with compression off. If = you are limited by the I/O bandwidth to your drives, then *if* your data = is highly compressible, then you will get better performance with = compression on. I have managed large pools of both data that compresses = well and data that does not. = http://wiki.illumos.org/display/illumos/ZFS+and+Advanced+Format+disks = discusses the issue and presents solutions using Illumos. I could find = no such examples for FreeBSD, but I'm sure some of the same techniques = would work (manually setting the ashift to 12 for 4K disks). -- Paul Kraus Deputy Technical Director, LoneStarCon 3 Sound Coordinator, Schenectady Light Opera Company