From owner-freebsd-fs@FreeBSD.ORG  Tue Jul 22 22:08:22 2008
Return-Path: <owner-freebsd-fs@FreeBSD.ORG>
Delivered-To: freebsd-fs@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 537D11065674
	for <freebsd-fs@freebsd.org>; Tue, 22 Jul 2008 22:08:22 +0000 (UTC)
	(envelope-from 000.fbsd@quip.cz)
Received: from elsa.codelab.cz (elsa.codelab.cz [91.103.162.4])
	by mx1.freebsd.org (Postfix) with ESMTP id 1F4E08FC12
	for <freebsd-fs@freebsd.org>; Tue, 22 Jul 2008 22:08:21 +0000 (UTC)
	(envelope-from 000.fbsd@quip.cz)
Received: from localhost (localhost.codelab.cz [127.0.0.1])
	by elsa.codelab.cz (Postfix) with ESMTP id 1ACBE19E023;
	Wed, 23 Jul 2008 00:08:20 +0200 (CEST)
Received: from [192.168.1.2] (r5bb235.net.upc.cz [86.49.61.235])
	(using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits))
	(No client certificate requested)
	by elsa.codelab.cz (Postfix) with ESMTPSA id 2108219E019;
	Wed, 23 Jul 2008 00:08:18 +0200 (CEST)
Message-ID: <48865A68.1010504@quip.cz>
Date: Wed, 23 Jul 2008 00:08:40 +0200
From: Miroslav Lachman <000.fbsd@quip.cz>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US;
	rv:1.7.12) Gecko/20050915
X-Accept-Language: cz, cs, en, en-us
MIME-Version: 1.0
To: Matt Simerson <matt@corp.spry.com>
References: <5E8D64DE-EC9B-4B11-BCB4-17BA63650BB7@corp.spry.com>
In-Reply-To: <5E8D64DE-EC9B-4B11-BCB4-17BA63650BB7@corp.spry.com>
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit
Cc: freebsd-fs@freebsd.org
Subject: Re: ZFS hang issue and prefetch_disable
X-BeenThere: freebsd-fs@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Filesystems <freebsd-fs.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-fs>,
	<mailto:freebsd-fs-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-fs>
List-Post: <mailto:freebsd-fs@freebsd.org>
List-Help: <mailto:freebsd-fs-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-fs>,
	<mailto:freebsd-fs-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Tue, 22 Jul 2008 22:08:22 -0000

Matt Simerson wrote:
> Symptoms
> 
> Deadlocks under heavy IO load on the ZFS file system with  
> prefetch_disable=0.  Setting vfs.zfs.prefetch_disable=1 results in a  
> stable system.

[...]

> With vfs.zfs.prefetch_disable=1, a hang will occur within a few hours  
> (no more than a day). If I keep the i/o load (measured via iostat)  down 
> to a low level (< 200 iops) then I still get hangs but less  frequently 
> (1-6 days).  The only way I have found to prevent the hangs  is by 
> setting vfs.zfs.prefetch_disable=1.

"With vfs.zfs.prefetch_disable=1, a hang will occur within...", did you 
realy mean prefetch_disable=1 in this sentence? Your whole e-mail seems 
that prefetch_disable=1 is good workaround, so I expect you have 
prefetch_disable=0 previously which causes hangs...

Miroslav Lachman