From owner-freebsd-fs@freebsd.org Sun Jul 3 22:24:59 2016 Return-Path: Delivered-To: freebsd-fs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id E6D00B905B2 for ; Sun, 3 Jul 2016 22:24:59 +0000 (UTC) (envelope-from jkh@ixsystems.com) Received: from barracuda.ixsystems.com (barracuda.ixsystems.com [12.229.62.30]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "*.ixsystems.com", Issuer "Go Daddy Secure Certificate Authority - G2" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id C83D02A55 for ; Sun, 3 Jul 2016 22:24:59 +0000 (UTC) (envelope-from jkh@ixsystems.com) X-ASG-Debug-ID: 1467584698-08ca0410fd47d10001-3nHGF7 Received: from zimbra.ixsystems.com ([10.246.0.20]) by barracuda.ixsystems.com with ESMTP id ZiIXz8PhNmTmsjwX (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Sun, 03 Jul 2016 15:24:58 -0700 (PDT) X-Barracuda-Envelope-From: jkh@ixsystems.com X-Barracuda-RBL-Trusted-Forwarder: 10.246.0.20 X-ASG-Whitelist: Client Received: from localhost (localhost [127.0.0.1]) by zimbra.ixsystems.com (Postfix) with ESMTP id 0E256CA22F0; Sun, 3 Jul 2016 15:24:58 -0700 (PDT) Received: from zimbra.ixsystems.com ([127.0.0.1]) by localhost (zimbra.ixsystems.com [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id Qj9rJWWKgSE0; Sun, 3 Jul 2016 15:24:57 -0700 (PDT) Received: from localhost (localhost [127.0.0.1]) by zimbra.ixsystems.com (Postfix) with ESMTP id 49C91CA2329; Sun, 3 Jul 2016 15:24:57 -0700 (PDT) X-Virus-Scanned: amavisd-new at ixsystems.com Received: from zimbra.ixsystems.com ([127.0.0.1]) by localhost (zimbra.ixsystems.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id WCLMZWVeGxpF; Sun, 3 Jul 2016 15:24:57 -0700 (PDT) Received: from [172.20.0.42] (vpn.ixsystems.com [10.249.0.2]) by zimbra.ixsystems.com (Postfix) with ESMTPSA id 01BF6CA22F0; Sun, 3 Jul 2016 15:24:56 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 9.3 \(3124\)) Subject: Re: HAST + ZFS + NFS + CARP From: Jordan Hubbard X-ASG-Orig-Subj: Re: HAST + ZFS + NFS + CARP In-Reply-To: <20160703214723.GF41276@mordor.lan> Date: Sun, 3 Jul 2016 15:24:56 -0700 Cc: Ben RUBSON , freebsd-fs@freebsd.org Content-Transfer-Encoding: quoted-printable Message-Id: <65906F84-CFFC-40E9-8236-56AFB6BE2DE1@ixsystems.com> References: <20160630144546.GB99997@mordor.lan> <71b8da1e-acb2-9d4e-5d11-20695aa5274a@internetx.com> <20160630153747.GB5695@mordor.lan> <63C07474-BDD5-42AA-BF4A-85A0E04D3CC2@gmail.com> <678321AB-A9F7-4890-A8C7-E20DFDC69137@gmail.com> <20160630185701.GD5695@mordor.lan> <6035AB85-8E62-4F0A-9FA8-125B31A7A387@gmail.com> <20160703192945.GE41276@mordor.lan> <20160703214723.GF41276@mordor.lan> To: Julien Cigar X-Mailer: Apple Mail (2.3124) X-Barracuda-Connect: UNKNOWN[10.246.0.20] X-Barracuda-Start-Time: 1467584698 X-Barracuda-Encrypted: ECDHE-RSA-AES256-GCM-SHA384 X-Barracuda-URL: https://10.246.0.26:443/cgi-mod/mark.cgi X-Virus-Scanned: by bsmtpd at ixsystems.com X-Barracuda-BRTS-Status: 1 X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 03 Jul 2016 22:25:00 -0000 > On Jul 3, 2016, at 2:47 PM, Julien Cigar = wrote: >=20 > I guess that ZFS will split the read requests accross all devices in > order to maximize performance... which could lead to contrary to what = is > expecpted when iSCSI disks are involved, no? > Is there some sysctl params which could prevent this unexpected > behavior? Nope. You will suffer the performance implications of layering a = filesystem that expects =E2=80=9Crotating media or SSDs=E2=80=9D (with = the innate ability to parallelize multiple requests in a way that ADD = performance) on top of a system which is now serializing the requests = across an internet connection to another software layer which may offer = no performance benefits to having multiple LUNs at all. You can try = iSCSI-specific tricks like MPIO to try and increase performance, but ZFS = itself is just going to treat everything it sees as =E2=80=9Ca disk=E2=80=9D= and so physical concepts like mirrors or multiple vdevs for performance = won=E2=80=99t translate across. Example question: What=E2=80=99s the point of writing multiple copies of = data across virtual disks in a mirror configuration if the underlying = storage for the virtual disks is already redundant and the I/Os to it = serialize? Example Answer: There is no point. In fact, it=E2=80=99s a = pessimization to do so. This is not a lot different than running ZFS on top of RAID controllers = that turn N physical disks into 1 or more virtual disks. You have to = make entirely different performance decisions based on such scenarios = and that=E2=80=99s just the way it is, which is also why we don=E2=80=99t = recommend doing that. - Jordan