From owner-freebsd-questions@FreeBSD.ORG Wed Dec 8 21:40:03 2010 Return-Path: Delivered-To: questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 812C4106564A for ; Wed, 8 Dec 2010 21:40:03 +0000 (UTC) (envelope-from cswiger@mac.com) Received: from asmtpout030.mac.com (asmtpout030.mac.com [17.148.16.105]) by mx1.freebsd.org (Postfix) with ESMTP id 6463D8FC1F for ; Wed, 8 Dec 2010 21:40:03 +0000 (UTC) MIME-version: 1.0 Content-transfer-encoding: 7BIT Content-type: text/plain; charset=us-ascii Received: from cswiger1.apple.com ([17.209.4.71]) by asmtp030.mac.com (Sun Java(tm) System Messaging Server 6.3-8.01 (built Dec 16 2008; 32bit)) with ESMTPSA id <0LD4000IKMQJQW50@asmtp030.mac.com> for questions@freebsd.org; Wed, 08 Dec 2010 12:39:56 -0800 (PST) X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 ipscore=0 suspectscore=0 phishscore=0 bulkscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx engine=6.0.2-1010190000 definitions=main-1012080123 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.2.15,1.0.148,0.0.0000 definitions=2010-12-08_10:2010-12-08, 2010-12-08, 1970-01-01 signatures=0 From: Chuck Swiger In-reply-to: Date: Wed, 08 Dec 2010 12:39:55 -0800 Message-id: References: To: Dave Cundiff X-Mailer: Apple Mail (2.1082) Cc: questions@freebsd.org Subject: Re: Terrible Clock Skew X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 08 Dec 2010 21:40:03 -0000 Hi, Dave-- On Dec 8, 2010, at 12:01 PM, Dave Cundiff wrote: > Hi everyone, > > I posted this to the forum as well but figured I'd try here since the > same people might not subscribe to both. I'm not sure which forum you're mentioning here, although it proves you right about the conclusion you'd made here. :-) > I've been experiencing some terrible clock skew and just can't figure > it out. By terrible I mean I'm losing 30 minutes a day. The loss only > occurs when I bring the system under heavy load. The load is multiple > Rsync backups to a ZFS pool(with gzip compression) backed by a 16 disk > Raid50. I'm using a hardware Raid controller for battery backed write > caching. That kind of slew rate is well past what ntpd can deal with; it suggests possibly that you're losing timer interrupts, or maybe that the "time of day" clock on the motherboard is broken or dead. Output of "vmstat -i" might be informative for the former, for the latter check whether the BIOS can keep the clock sane while in the BIOS menu-- there should be a small Li battery on the motherboard which might be replaceable. You might also double-check that you've got the latest BIOS version update, but that's less likely to help. For a workaround, you can fire off "ntpdate -b" from cron every 5 minutes or similar to keep the clock from drifting too far. Regards, -- -Chuck