From owner-freebsd-current@FreeBSD.ORG Thu Nov 12 21:15:10 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 C6ED3106568B; Thu, 12 Nov 2009 21:15:10 +0000 (UTC) (envelope-from sullrich@gmail.com) Received: from ey-out-2122.google.com (ey-out-2122.google.com [74.125.78.26]) by mx1.freebsd.org (Postfix) with ESMTP id 2C74A8FC29; Thu, 12 Nov 2009 21:15:09 +0000 (UTC) Received: by ey-out-2122.google.com with SMTP id 9so675325eyd.9 for ; Thu, 12 Nov 2009 13:15:09 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :from:date:message-id:subject:to:cc:content-type; bh=XPxhyjpCyDKtvVOp4CgEwsooV0aAfOyV7mkFa+1x7QI=; b=l6jaSz2RP5ZExxE5sQNUH4SnBlsUrUBVwvIZwGM9hKCYodYBF00bPMERGiSDqfj2rY fW+n3zz//cgODgInIPEIeYcvGysBkD/UqxuO5uPD73aQnzlnxPHoGc/5BuH+g74zr5eu Q2d1AQyu0RNz/t25MWiDPh04xydRlRFGuqn0o= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type; b=Ot3iyQQRL6BNZLaGFkZlIo1eYjiH/rOyBCUJSo+Vcty6Lcz4pVH6f+wVo2Z4j3pP1h gomhA/SWEOCtrE4u1+WRT09ocpnV/C/vf3nE0YAjOnodwK6KHm6zrr7ruomcNPSp7AOs vO+AGec5rmrSnMHNcyGhGlTWnRXSvGHa5R9nU= MIME-Version: 1.0 Received: by 10.213.23.78 with SMTP id q14mr2072848ebb.80.1258060509085; Thu, 12 Nov 2009 13:15:09 -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: Scott Ullrich Date: Thu, 12 Nov 2009 16:14:49 -0500 Message-ID: To: Artem Belevich Content-Type: text/plain; charset=ISO-8859-1 Cc: "Sam Fourman Jr." , Rick Macklem , Dan Nelson , Ivan Voras , 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 21:15:10 -0000 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. 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. Scott