From owner-freebsd-fs@FreeBSD.ORG Fri Jan 10 15:07:12 2014 Return-Path: Delivered-To: freebsd-fs@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 677F74DC for ; Fri, 10 Jan 2014 15:07:12 +0000 (UTC) Received: from smarthost1.greenhost.nl (smarthost1.greenhost.nl [195.190.28.81]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id 24497134B for ; Fri, 10 Jan 2014 15:07:11 +0000 (UTC) Received: from smtp.greenhost.nl ([213.108.104.138]) by smarthost1.greenhost.nl with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.72) (envelope-from ) id 1W1dfx-0002KG-9J for freebsd-fs@freebsd.org; Fri, 10 Jan 2014 16:07:09 +0100 Content-Type: text/plain; charset=iso-8859-15; format=flowed; delsp=yes To: freebsd-fs@freebsd.org Subject: Re: What does ZFS write when nothing should write there? References: <52CFA0B6.7090109@fsn.hu> <52CFF18F.5040809@fsn.hu> <29BFE2939CF14317A149D6C2D68D9A8E@multiplay.co.uk> <52D00143.9060603@fsn.hu> Date: Fri, 10 Jan 2014 16:05:51 +0100 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit From: "Ronald Klop" Message-ID: In-Reply-To: <52D00143.9060603@fsn.hu> User-Agent: Opera Mail/12.16 (Win32) X-Authenticated-As-Hash: 398f5522cb258ce43cb679602f8cfe8b62a256d1 X-Virus-Scanned: by clamav at smarthost1.samage.net X-Spam-Level: / X-Spam-Score: -0.5 X-Spam-Status: No, score=-0.5 required=5.0 tests=BAYES_05 autolearn=disabled version=3.3.1 X-Scan-Signature: e462de357cb394d64966911c06262bc8 X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.17 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 10 Jan 2014 15:07:12 -0000 On Fri, 10 Jan 2014 15:18:43 +0100, Attila Nagy wrote: > On 01/10/14 14:29, Dmitry Morozovsky wrote: >> On Fri, 10 Jan 2014, Steven Hartland wrote: >> >>>>>> I've created 6 zpools, each of them with zpool create -m /data/A >>>>>> dataA >>>>>> mirror >>>>>> daX daY. >>>>>> The machine has nothing running except sshd and my shell. >>>>>> >>>>>> Yet, I see this in gstat: >>>>> [snip] >>>>> >>>>>> 0 88 0 0 0.0 82 573 4.1 9.0 da5 >>>>>> 0 89 0 0 0.0 83 573 4.8 9.8 da6 >>>>>> 0 87 0 0 0.0 81 573 2.6 5.7 da9 >>>>>> 0 89 0 0 0.0 84 573 3.0 6.7 da10 >>>>> Did you turn off atime? >>>>> >>>> No, but how does it matter? >>>> The process list is the following: init, getty, sshd, csh and the >>>> pool is >>>> completely empty. >>> With atime on each time you access a file it will update its "atime" >>> hence causing writes. >>> >>> We use atime=off at the pool level on all machines to avoid that >>> zfs set atime=off >> BTW, it seems that ZFS updates atime of some inodes (root one?) on >> every kernel >> update thread invocation even when completely empty -- is it correct >> behaviour? >> > Because there are no files, it must (?) be the root. But at this > frequency? Some dtrace commands might give enlightenment. Ronald