From owner-freebsd-current@FreeBSD.ORG Thu Nov 12 20:19:40 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 EDF5E106566C for ; Thu, 12 Nov 2009 20:19:40 +0000 (UTC) (envelope-from artemb@gmail.com) Received: from mail-iw0-f190.google.com (mail-iw0-f190.google.com [209.85.223.190]) by mx1.freebsd.org (Postfix) with ESMTP id 9E36A8FC0C for ; Thu, 12 Nov 2009 20:19:40 +0000 (UTC) Received: by iwn28 with SMTP id 28so2087475iwn.3 for ; Thu, 12 Nov 2009 12:19:40 -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:date:x-google-sender-auth:message-id:subject:from:to:cc :content-type; bh=6mCrYovx1tkaPaPMAbSC4yXMVEThA/MIeCvZVbrlqF0=; b=A4jLh/qeI4bE14/bZ7r0dJvPq7B5ciw8rxuUpkKyBByw8l7mCXY6sJgtOubRUb7Xx8 iirjq5V2gROrUsHonv6BNkql8YVeiW9y5YOk/K2YOSpmeJRgVDzeTqc+YCYehTcmVBSM 9WQVDM/dXqvN4ehJvJGWF8PqdAB70U/219rJU= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type; b=o1tL7sohPzzjIsIZ/WZ190Ep3KsFAo4XVR+SObBvRkOdAYjTKX6Zvqa1oRohcIPRGM 9x+UJ5hNK3v9Ed5ei1CjPfJZchU6hBodRnzdtv6xK4hEyTipDNEFC0IvFHElDBizXDzM l5A5auULDOQVuXcGXMGiome/6Ad2rfsLrUHw0= MIME-Version: 1.0 Sender: artemb@gmail.com Received: by 10.231.6.153 with SMTP id 25mr283269ibz.54.1258057180022; Thu, 12 Nov 2009 12:19:40 -0800 (PST) In-Reply-To: <11167f520911121101o403751ddmb544dfaf1c61bf1e@mail.gmail.com> 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> Date: Thu, 12 Nov 2009 12:19:39 -0800 X-Google-Sender-Auth: b225fa60e14c2835 Message-ID: From: Artem Belevich To: "Sam Fourman Jr." Content-Type: text/plain; charset=ISO-8859-1 Cc: Rick Macklem , Dan Nelson , Ivan Voras , freebsd-current@freebsd.org, Scott Ullrich 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 20:19:41 -0000 > is there anyway to safely have a log device on a ramdisk? I would assume not. 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. --Artem