From owner-freebsd-fs@freebsd.org Fri Aug 10 14:54:14 2018 Return-Path: Delivered-To: freebsd-fs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 1D715106D2AF for ; Fri, 10 Aug 2018 14:54:14 +0000 (UTC) (envelope-from devgs@ukr.net) Received: from frv199.fwdcdn.com (frv199.fwdcdn.com [212.42.77.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "*.ukr.net", Issuer "Thawte RSA CA 2018" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id AF3558E496 for ; Fri, 10 Aug 2018 14:54:13 +0000 (UTC) (envelope-from devgs@ukr.net) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=ukr.net; s=ffe; h=Content-Transfer-Encoding:Content-Type:MIME-Version:References: In-Reply-To:Message-Id:Cc:To:Subject:From:Date:Sender:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=L7hqS2GHlyGm4BXR7rjnF03dtxM5bEa2LXAsKb1uImE=; b=UKp07mgJ1319InaKmxVr/RHeqx VCeb/9+OQW0M9qACXYXHfyJiSmoI3QhcEYGK+oVaeRH2iy9/kQQCDZIOKIDLo78FQzTYQMk0ToZOL ThdyhFFCRSWBiXskthvUMkWcAPiv3JCfT+1NCtnh1k05PRf8ZNFDLIfQeTl16+r2zrXY=; Received: from [10.10.10.33] (helo=frv33.fwdcdn.com) by frv199.fwdcdn.com with smtp ID 1fo8nk-000JLg-4x for freebsd-fs@freebsd.org; Fri, 10 Aug 2018 17:54:04 +0300 Date: Fri, 10 Aug 2018 17:54:03 +0300 From: Paul Subject: Re[2]: Question regarding relevance of syncer(4) in the context of ZFS To: Konstantin Belousov Cc: freebsd-fs@freebsd.org X-Mailer: mail.ukr.net 5.0 Message-Id: <1533912779.505892598.lhqtiahk@frv33.fwdcdn.com> In-Reply-To: <20180810143940.GC2649@kib.kiev.ua> References: <1533910747.525373107.k9z2n7hj@frv33.fwdcdn.com> <20180810143940.GC2649@kib.kiev.ua> X-Reply-Action: reply Received: from devgs@ukr.net by frv33.fwdcdn.com; Fri, 10 Aug 2018 17:54:04 +0300 MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: binary X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.27 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 10 Aug 2018 14:54:14 -0000 10 August 2018, 17:39:52, by "Konstantin Belousov" : > On Fri, Aug 10, 2018 at 05:28:11PM +0300, Paul wrote: > > Hello team, > > > > > > If my understanding is correct then ZFS does not need to be pushed around and being told when to sync data to devices. > > It is perfectly capable of keeping data consistent and synchronized according to configured options. > > > > We even disable 'sync' option of file system that we use. But unfortunately we see a constant and periodical spikes > > of load on our servers that are directly related to wake-ups of 'syncer' kernel daemon. Is it safe to assume that > > 'syncer' is not necessary on configurations that only use ZFS, and no other file systems? And hence, is it safe > > to assume that setting all of 'kern.filedelay', 'kern.dirdelay' and 'kern.metadelay' to some large values will not > > compromise system's durability? > > One of the job of the syncer is to convert dirty user-mapped pages into > the filesystem-specific write requests. Without syncer touching the mount > point, corresponding pages could linger forever, or at least until a memory > pressure causes pagedaemon to clean them. Thanks a lot for clarification! I didn't think about dirty user-mapped pages... Best regards, Paul