From owner-freebsd-fs@FreeBSD.ORG Sun Jun 21 22:51:31 2009 Return-Path: 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 660D9106564A for ; Sun, 21 Jun 2009 22:51:31 +0000 (UTC) (envelope-from andrew@modulus.org) Received: from email.octopus.com.au (email.octopus.com.au [122.100.2.232]) by mx1.freebsd.org (Postfix) with ESMTP id 2532A8FC1B for ; Sun, 21 Jun 2009 22:51:30 +0000 (UTC) (envelope-from andrew@modulus.org) Received: by email.octopus.com.au (Postfix, from userid 1002) id E46BB17D4C; Mon, 22 Jun 2009 08:51:52 +1000 (EST) X-Spam-Checker-Version: SpamAssassin 3.2.3 (2007-08-08) on email.octopus.com.au X-Spam-Level: X-Spam-Status: No, score=-1.4 required=10.0 tests=ALL_TRUSTED autolearn=failed version=3.2.3 Received: from [10.1.50.60] (ppp121-44-41-14.lns10.syd7.internode.on.net [121.44.41.14]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: admin@email.octopus.com.au) by email.octopus.com.au (Postfix) with ESMTP id 6E1CE1717D; Mon, 22 Jun 2009 08:51:46 +1000 (EST) Message-ID: <4A3EB902.8080503@modulus.org> Date: Mon, 22 Jun 2009 08:49:38 +1000 From: Andrew Snow User-Agent: Thunderbird 2.0.0.14 (X11/20080523) MIME-Version: 1.0 To: Dan Naumov , freebsd-fs@freebsd.org References: <570433.20373.qm@web37308.mail.mud.yahoo.com> <4A3E9D81.1060406@modulus.org> In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: Subject: Re: ufs2 / softupdates / ZFS / disk write cache X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 21 Jun 2009 22:51:31 -0000 Dan Naumov wrote: >>> Or: >>> B) use SCSI instead of ATA disks >>> C) use UFS+gjournal instead of UFS+SU >>> D) use ZFS instead of UFS+SU >> All of these solutions still involve disabling of write cache, with a performance hit of varying degrees. (I have tried all of those except gjournal!) B) SCSI drives come with write caching disabled by default. But here, the performance loss is partially made up by Tagged Command Queueing and faster spindle speeds C) gjournal needs to flush the disk cache regularly to maintain consistence. It doesn't need to do it as often but on a write-heavy system it isn't ideal for performance because it flushes everything in the cache and not just the journal. D) ZFS - same as (C) > who on earth is going to accept 2-4 MB/s write speeds from > a modern disk in 2009? eg. remote headless systems which don't do much (DNS server) :-) - Andrew