From owner-freebsd-fs@FreeBSD.ORG Fri Feb 20 13:30:04 2015 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id CC1303A3 for ; Fri, 20 Feb 2015 13:30:04 +0000 (UTC) Received: from forward3h.mail.yandex.net (forward3h.mail.yandex.net [IPv6:2a02:6b8:0:f05::3]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "forwards.mail.yandex.net", Issuer "Certum Level IV CA" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 802929FF for ; Fri, 20 Feb 2015 13:30:04 +0000 (UTC) Received: from web18h.yandex.ru (web18h.yandex.ru [84.201.186.47]) by forward3h.mail.yandex.net (Yandex) with ESMTP id 207AE1362D3A for ; Fri, 20 Feb 2015 16:29:26 +0300 (MSK) Received: from 127.0.0.1 (localhost [127.0.0.1]) by web18h.yandex.ru (Yandex) with ESMTP id AE0294F61593; Fri, 20 Feb 2015 16:29:26 +0300 (MSK) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex.ru; s=mail; t=1424438966; bh=xwsPfmonLqvZvt5FGFwk7/PH5MPzCOm8mwhqlqDEa04=; h=From:To:In-Reply-To:References:Subject:Date; b=YiHO4+gNTyXqtN+132xvIKFdt3kxiaPog/WF+tSaGitETO2TbGERVSnT2JXhBBm+Z mVuU97q1nNET6SwRPz3tIv06phGC6/8hO3SKDzqraG4JAXWsAjCCH9V/PFEcJuKT8x J/kSBjTDj766Lsz84LNO3ZWsQAZHjT50/hd5KASc= Received: by web18h.yandex.ru with HTTP; Fri, 20 Feb 2015 16:29:26 +0300 From: Ilya A. Arkhipov To: "freebsd-fs@freebsd.org" In-Reply-To: <66c5011b.0fcc09f9@fabiankeil.de> References: <54E71E20.8080303@yandex.ru> <66c5011b.0fcc09f9@fabiankeil.de> Subject: Re: Disable zfs prefetch by default MIME-Version: 1.0 Message-Id: <614751424438966@web18h.yandex.ru> X-Mailer: Yamail [ http://yandex.ru ] 5.0 Date: Fri, 20 Feb 2015 16:29:26 +0300 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=koi8-r X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 20 Feb 2015 13:30:04 -0000 20.02.2015, 15:52, "Fabian Keil" : > "Ilya A. Arkhipov" wrote: >> šWe have zfs prefetch enabled by default with > 4GB, but I didn't seen >> šany case for using it, and all tuning guide saying to disable it. > > Which tuning guides are you referring to? This one https://wiki.freebsd.org/ZFSTuningGuide >> šMaybe we disable zfs prefetch by default ? Or could you please provide >> šwhy it needed. > > Whether or not prefetching is useful depends on the workload > and the setup. > > If you doubt that the prefetch default is useful for your workload > (for example because your systems mainly do small "random" reads > from "random" files), you can easily test this by disabling prefetching > for a while. > > If this is too much work (or if no difference can be measured), > the default is probably fine. > > Fabian Actualy on all my servers(more 300 ^_^), I've disable prefetch because on all have the same issue: http://i.imgur.com/aJNCiBK.png http://i.imgur.com/Di3FuWw.png http://i.imgur.com/uunH1k8.png http://i.imgur.com/vjYiB2K.png -- With Best Regards, Ilya A. Arkhipov