From owner-freebsd-fs@FreeBSD.ORG Wed Jul 9 07:21:20 2014 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 24C15362 for ; Wed, 9 Jul 2014 07:21:20 +0000 (UTC) Received: from mail-qa0-x229.google.com (mail-qa0-x229.google.com [IPv6:2607:f8b0:400d:c00::229]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id DBC3D2B61 for ; Wed, 9 Jul 2014 07:21:19 +0000 (UTC) Received: by mail-qa0-f41.google.com with SMTP id cm18so5843180qab.14 for ; Wed, 09 Jul 2014 00:21:19 -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=nQv3dBegLuJa0UNx+Tvjr2DVvwdsMG9knQPbwB60Wxg=; b=rD+BPrvAC/OlL+T0BaEhsXcVdnlcxlJJOeTtKYhg5caMsGUN/q6TjGyhYddGQCx3zJ I/OI9/g71V8HTlndXB0sWeo1C9RIZ61fiyBzyNrV4GVoCa7IoQ6vhV/3by9ROq6y6JgG QZG+yKATf66fHFX81wUz2muEOyGePv1lzGXfISBbltsl0AsT35547jN7x1wqdvOoYMn1 jPISafbf4Rcs6jn22AsTD5T6SacEjkMu0GIOyfEO78CXxmFlkAzTd7Lkn1T5BEPjfcKY FQ/SU9jNmQeLqEMSjME2K3Ev3rXZtwWMuQYHzATmey2i1OFNoloBTHe3RS+c2VdNF/FY U3rw== MIME-Version: 1.0 X-Received: by 10.224.172.201 with SMTP id m9mr67912263qaz.32.1404890478951; Wed, 09 Jul 2014 00:21:18 -0700 (PDT) Received: by 10.96.13.133 with HTTP; Wed, 9 Jul 2014 00:21:18 -0700 (PDT) In-Reply-To: <20140708025106.GA85067@neutralgood.org> References: <20140708025106.GA85067@neutralgood.org> Date: Wed, 9 Jul 2014 08:21:18 +0100 Message-ID: Subject: Re: Using 2 SSD's to create a SLOG From: krad To: kpneal@pobox.com Content-Type: text/plain; charset=UTF-8 X-Content-Filtered-By: Mailman/MimeDel 2.1.18 Cc: FreeBSD Filesystems X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 09 Jul 2014 07:21:20 -0000 An NFS server is a common task that generates lots of synchronous writes On 8 July 2014 03:51, wrote: > On Mon, Jul 07, 2014 at 06:06:43PM -0700, javocado wrote: > > I am interested in adding an SSD "SLOG" to my ZFS system so as to > > (dramatically) speed up writes on this system. > > > > My question is if ZFS will, itself, internally, mirror two SSDs that are > > used as a SLOG ? > > > > What I mean is, if ZFS is already smart enough to create a zpool mirror > > (or, on my case, a zpool raidz3) then perhaps ZFS is also smart enough to > > mirror the SLOG to two individual SSDs ? > > > > I am hoping to dumbly plug two SSDs onto motherboard SATA ports and just > > hand them over, raw, to ZFS. > > From the zpool man page: > > Example 12 Creating a ZFS Pool with Mirrored Separate Intent Logs > > The following command creates a ZFS storage pool consisting of > two, > two-way mirrors and mirrored log devices: > > # zpool create pool mirror c0d0 c1d0 mirror c2d0 c3d0 log mirror \ > c4d0 c5d0 > > You should be able to use that example to make the 'zpool add' command to > add the mirrored log to an existing pool. > > But know that the SLOG only helps writes that are synchronous. This is in > many workloads a small fraction of the total writes. For other workloads > it is a large portion of the writes. > > Do you know for certain that you need a SLOG? > -- > Kevin P. Neal http://www.pobox.com/~kpn/ > On the community of supercomputer fans: > "But what we lack in size we make up for in eccentricity." > from Steve Gombosi, comp.sys.super, 31 Jul 2000 11:22:43 -0600 > _______________________________________________ > freebsd-fs@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-fs > To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org" >