From owner-freebsd-stable@FreeBSD.ORG Wed Mar 9 14:01:47 2011 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 44353106564A for ; Wed, 9 Mar 2011 14:01:47 +0000 (UTC) (envelope-from matthias.andree@gmx.de) Received: from mailout-de.gmx.net (mailout-de.gmx.net [213.165.64.22]) by mx1.freebsd.org (Postfix) with SMTP id A3F1D8FC1B for ; Wed, 9 Mar 2011 14:01:46 +0000 (UTC) Received: (qmail invoked by alias); 09 Mar 2011 14:01:44 -0000 Received: from g230081165.adsl.alicedsl.de (EHLO [192.168.0.4]) [92.230.81.165] by mail.gmx.net (mp006) with SMTP; 09 Mar 2011 15:01:44 +0100 X-Authenticated: #428038 X-Provags-ID: V01U2FsdGVkX1/Eu71xx2LEvyZkFSSreYdtnXCNw6SeCz4lgXiPMc 5f8VGPxPDS6raS Message-ID: <4D778846.3080008@gmx.de> Date: Wed, 09 Mar 2011 15:01:42 +0100 From: Matthias Andree User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv:1.9.2.15) Gecko/20110303 Mnenhy/0.8.3 Thunderbird/3.1.9 MIME-Version: 1.0 To: freebsd-stable@freebsd.org References: <20110308114810.GA37554@icarus.home.lan> <4D775CF1.1010501@gmx.de> <20110309125132.GB62338@icarus.home.lan> In-Reply-To: X-Enigmail-Version: 1.1.1 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Y-GMX-Trusted: 0 Cc: Jeremy Chadwick Subject: Re: ZFS performance as the FS fills up? X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 09 Mar 2011 14:01:47 -0000 Am 09.03.2011 14:28, schrieb Tom Evans: > On Wed, Mar 9, 2011 at 12:51 PM, Jeremy Chadwick > wrote: >> >> Otherwise, I can imagine that prefetching could cause what you describe, >> which is enabled by default in 8.0 and 8.1 and auto-disables in 8.2 if >> the amount of available memory is less than 4GB. >> > > I don't think this is accurate. Prefetch was certainly disabled by > default on 8.0 if you had 4GB of RAM or less, requiring the sysctl > vfs.zfs.prefetch_disable=0 to be set if you wanted prefetch and had > 4GB of RAM or less. Personally I've got a 4 GB amd64 setup, had been on RELENG_8 aka 8-STABLE before 8.2-RELEASE (and use RELENG_8_2 aka 8.2-RELEASE now), and I had tried vfs.zfs.prefetch_disable either way without seeing a big difference in sluggish performance (and actually even moved out /usr/home to a UFS file system to get somewhat back up to speed). I suppose that fragmentation was a big issue but cannot confirm that now. However, I cannot produce the data Jeremy has asked for any more, as the incriminated file system no longer exists. I recall ZFS (even the earlier versions before the bigger version leap) was very responsive when it was less than 50% full. I have, however, collected and reformatted (for Wiki) Jeremy's list at - we'd need to review this and once deemed suitable, link it from the ZFS and possibly ZFSTuningGuide pages, and possibly also from the FreeBSD ZFS manual pages. HTH Matthias -- Matthias Andree