From owner-freebsd-questions@FreeBSD.ORG Mon Jul 21 15:16:24 2014 Return-Path: Delivered-To: freebsd-questions@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 6A58DAE4 for ; Mon, 21 Jul 2014 15:16:24 +0000 (UTC) Received: from mail-qa0-f46.google.com (mail-qa0-f46.google.com [209.85.216.46]) (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 2A19020CE for ; Mon, 21 Jul 2014 15:16:23 +0000 (UTC) Received: by mail-qa0-f46.google.com with SMTP id v10so5262061qac.33 for ; Mon, 21 Jul 2014 08:16:16 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:content-type:content-transfer-encoding:date :subject:to:message-id:mime-version; bh=R65s+y54kOIZhdWYfCXKo0YpAE9uGZ5xkgWgTonVTKc=; b=WLEOP6AENiShZtq/zQlwDDmbLhSZZKr0olwxMM1249jUeM/1RUe+pG3ItD9RsYGQED fmKfEGOsjyCSpj6ZW86yUpzVNQui9NXZz7URDBmvOsyYNxhrH9zJvG3/NO1CTHoje1ED CG3QzE3aKm8NgTPcAwXuM2ec8B58G5+t/ZVDX4o9w8+Q/SavFglurB4rDYNWWFispdt3 qjVbLsEpqntAA+f+jbl8HoiOpyCs4V2RbtRyMrlCpIOyw1Bq8MlyWo7tStU1tqPRENfO edyuRkZ0RneQnOU4Nb0K2Bl0EVXVaGUoUIzNEXSmYgAGkqUDHbawXkuKc1sv06bJOhLu 7G6g== X-Gm-Message-State: ALoCoQmydyTVWX0z9hLK/T7s+eJszDCOYmt7aEYyKCE2lSOZc8Yo3Ot9/cfzOKqs476VTv453m9M X-Received: by 10.140.95.101 with SMTP id h92mr40146883qge.35.1405955776385; Mon, 21 Jul 2014 08:16:16 -0700 (PDT) Received: from [192.168.2.65] ([96.236.21.80]) by mx.google.com with ESMTPSA id w3sm3025589qap.37.2014.07.21.08.16.15 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 21 Jul 2014 08:16:15 -0700 (PDT) From: Paul Kraus Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Date: Mon, 21 Jul 2014 11:16:13 -0400 Subject: SWAP / ZFS / SSD question To: freebsd-questions@freebsd.org Message-Id: Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) X-Mailer: Apple Mail (2.1878.6) X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 21 Jul 2014 15:16:24 -0000 Hi all, I=92ve got a box running Freebsd 9.1 with VirtualBox and have = run into a couple odd hangs. The system is a SuperMicro with two = quad-core Xeon, 32GB RAM, and 3 1TB SAS drives mirrored via an internal = LSI 2208 controller (the drives are in JBOD mode) via ZFS. The system = is all ZFS with a 32GB zvol for swap. I am occasionally running into the dreaded "kernel: swap_pager: = indefinite wait buffer: bufobj: 0=94 issue. In the past it was always = when I was either adding a VM or changing a VM=92s configuration. I = assumed low RAM. But it hit last night (at 03:00 this morning in fact) = and nothing was changing at that time. There was about 770MB RAM free = and the ZFS ARC was using about 4GB, so the system was not really under = heavy memory pressure at the time. In order to reduce the impact, until we put a more permanent fix = in place, I have set sync=3Ddisable for the zvol =85 I figure that if = the system crashes and I lose a swap write I really don=92t care (I am = assuming here that swapd commits it=92s writes as sync). Our long term plan is a change in overall architecture that will = separate storage and compute services and have multiple compute nodes. = We started with one box assuming we would grown to more than one as the = business need arose. So our mid-term plan is to install a dedicated swap = device. The question is whether swapd (under 9.1) will be happy with an = SSD or whether there are unintended consequences to that route. Small = SSDs are cheap enough these days, we really don=92t need more than 32GB = (64GB if we are feeling extravagant). I know about the major performance differences between SSD = vendors and models (I heard all about that on the various ZFS lists I = subscribe to), so we will have to choose an SSD carefully. -- Paul Kraus paul@kraus-haus.org