From owner-freebsd-questions@FreeBSD.ORG Mon May 12 12:01:19 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 A919097C for ; Mon, 12 May 2014 12:01:19 +0000 (UTC) Received: from mail-wi0-x229.google.com (mail-wi0-x229.google.com [IPv6:2a00:1450:400c:c05::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 421F12DFD for ; Mon, 12 May 2014 12:01:19 +0000 (UTC) Received: by mail-wi0-f169.google.com with SMTP id hi2so5361547wib.0 for ; Mon, 12 May 2014 05:01:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:reply-to:in-reply-to:references:date:message-id :subject:from:to:cc:content-type; bh=H+cNPAYWIkofuFydfV2u/hLHIFqbx4YKeVLOkWYPi4A=; b=nDI1SQP4itqX+EDg1tAks6SjZbi2e3eErLD/mzouveiXKsxYQ0zjQ+QiqcZ46YhBCe aLWFbtUruWn1kt1eP4gqyQ855LC8mnyWbO/tHv3C5WFg7x7nWPk/q1OSc+x/X16I610u GuZmgRmlAQ0ozRz3F5CrvYD7AKYlElwog+BbWAPCuKLll6iLktCyP/+x0RElK/P/HBGl SXqe8B6n5A9nsx3wuphjQoZ/8Os1x96JK/lt78XP/JA7K2G6ScFwRGQQE43j43bauGe7 OclmJhzMFVkB/apOIMQagBqbrOjYtdg7MYgfskSpAeI/cyODt9SGQ+KG303vDGjIvv7D 2aSA== MIME-Version: 1.0 X-Received: by 10.194.92.81 with SMTP id ck17mr21325984wjb.14.1399896077488; Mon, 12 May 2014 05:01:17 -0700 (PDT) Received: by 10.217.43.194 with HTTP; Mon, 12 May 2014 05:01:17 -0700 (PDT) Reply-To: David.I.Noel@gmail.com In-Reply-To: References: <53697D8B.2060906@gmail.com> <5369B4A1.40506@gmail.com> <5369B8A3.7020403@my.hennepintech.edu> <5369C376.7000307@gmail.com> <5369C434.1090409@my.hennepintech.edu> Date: Mon, 12 May 2014 07:01:17 -0500 Message-ID: Subject: Re: Swap on ZFS From: David Noel To: krad Content-Type: text/plain; charset=UTF-8 Cc: Andrew Berg , FreeBSD Questions 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, 12 May 2014 12:01:19 -0000 > the check summing of swap is quite a big deal in my opinion. You have your > nice big server with ECC ram, but you do need to page some stuff in and > out. Now you go and get some corruption on your disks, which you then feed > back into your ram making the ecc irrelevant. Now that, I think, is a very interesting point, and one I hadn't considered. I see a great deal of value in having checksumming enabled on a swap volume/partition. What is the default behavior when I create a freebsd-swap partition with gpart, then hand it to the OS with swapon? Is there any sort of error correction mechanism in place? That alone would make a very strong case for swap on ZFS. However, I don't see any way around the rumored issue of the system hanging every time all my RAM is in use and I need to hit swap. Is this still the default behavior? The wiki says yes. I suppose I could test it myself fairly easily. But what would the solution be? If I test it and it hangs I'd like to be able to suggest a solution in the PR. Would adding a tunable that allowed me to reserve x MB for ZFS be the solution? Out of curiousity, what would that value need to be set to? How much memory does ZFS need available to write to disk?