From owner-freebsd-current@FreeBSD.ORG Thu Nov 12 21:29:16 2009 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id B550A1065694 for ; Thu, 12 Nov 2009 21:29:16 +0000 (UTC) (envelope-from ivoras@gmail.com) Received: from mail-bw0-f213.google.com (mail-bw0-f213.google.com [209.85.218.213]) by mx1.freebsd.org (Postfix) with ESMTP id 3C5408FC1A for ; Thu, 12 Nov 2009 21:29:16 +0000 (UTC) Received: by bwz5 with SMTP id 5so2859776bwz.3 for ; Thu, 12 Nov 2009 13:29:15 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:sender:received:in-reply-to :references:from:date:x-google-sender-auth:message-id:subject:to:cc :content-type:content-transfer-encoding; bh=1SNHzAvm54KCb5ReIk0MMLW2+oKG+zZlbuyrgBr6tEU=; b=OgU1MxY1wwKbId/3ucsDC/z+ACziJawKL/e1u1fpOR+7cnYgqTvL0G33xoW3VrT9sX cbIqClR4UVAT65aP3W56sgkMU3VFY1E3dWuuQFG9BiwJoaRNBGz1fNVJD/W2yBQLO3kH czmZtUubT+yoAfIu6GBKNJ6dKhaJK6DC/54aM= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:from:date :x-google-sender-auth:message-id:subject:to:cc:content-type :content-transfer-encoding; b=fyJv8ltw7RhZBf/1yhlD0NXLaTqVQaI0AusqhG0VMFC761RJsk8ibbvwC97vVh6b0O hZtyNvo80aVi5De1CKgUfWLbX4S6cyVoMKSIiQBHNCSzT1F+L5qeONCyrlcazrHeIulM 90FdKy/V5HfoYsaS6WXzj9SKhylryxS51FYLI= MIME-Version: 1.0 Sender: ivoras@gmail.com Received: by 10.216.90.9 with SMTP id d9mr1123040wef.201.1258061355107; Thu, 12 Nov 2009 13:29:15 -0800 (PST) In-Reply-To: References: <11167f520911111050j36dd94far667c81e6f5c18e69@mail.gmail.com> <20091111204903.GI89052@dan.emsphone.com> <11167f520911111326v13bb442bt36e853afbecdf834@mail.gmail.com> <9bbcef730911111352t12188bdajbca71bcf35a5beb5@mail.gmail.com> <11167f520911121044l74744c30u5a4d9ca008ab863c@mail.gmail.com> <11167f520911121101o403751ddmb544dfaf1c61bf1e@mail.gmail.com> From: Ivan Voras Date: Thu, 12 Nov 2009 22:28:55 +0100 X-Google-Sender-Auth: 3711550f5db4cf83 Message-ID: <9bbcef730911121328t342b2268oceba3712b52511d4@mail.gmail.com> To: Scott Ullrich Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Cc: freebsd-current@freebsd.org Subject: Re: Help ZFS FreeBSD 8.0 RC2 Write performance issue X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 12 Nov 2009 21:29:16 -0000 2009/11/12 Scott Ullrich : > On Thu, Nov 12, 2009 at 3:19 PM, Artem Belevich wrote: >> >> Log seems to be somewhat weak point in ZFS. If you lose your log >> device, you will lose your pool. Plus, there's no way to remove log >> device from the pool. So, once you attach some device as a log, you'd >> better be sure that device does not disappear, because it will take >> the rest of the pool with it. From that point, real ram-disk (i.e. >> /dev/mdN) is definitely a recipe for disaster. External ramdisk with a >> battery backup may be an option, but even in mirrored configuration >> seems rather risky to me. >> >> http://jmlittle.blogspot.com/2008/05/problem-with-slogs-how-i-lost.html >> >> I'd say that SSD are probably the best fit for slog role. > > Indeed. =C2=A0 I mirrored 2 SSDs on an Areca in case I loose one of them. > Partitioned the SSD into a log device and the rest being cache (see > the ZFS best practices guide for details). > > Needless to say my performance matches that of normal writes and reads > when using NFS now. So in short, you are saying the to get "normal" performance out of ZFS+NFS, the best way is to invest in an Areca and 2 SSDs :))