From owner-freebsd-fs@FreeBSD.ORG Thu Mar 29 20:13:02 2012 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 EA7211065673 for ; Thu, 29 Mar 2012 20:13:02 +0000 (UTC) (envelope-from rmacklem@uoguelph.ca) Received: from esa-jnhn.mail.uoguelph.ca (esa-jnhn.mail.uoguelph.ca [131.104.91.44]) by mx1.freebsd.org (Postfix) with ESMTP id A34068FC14 for ; Thu, 29 Mar 2012 20:13:02 +0000 (UTC) X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: Ap4EAHPBdE+DaFvO/2dsb2JhbABEhUS0VoIJAQEEASNWBRYOCgICDRkCWQYTCYd8BQupG5IqgS+ORoEYBJVhkC6DAw X-IronPort-AV: E=Sophos;i="4.75,338,1330923600"; d="scan'208";a="165858640" Received: from erie.cs.uoguelph.ca (HELO zcs3.mail.uoguelph.ca) ([131.104.91.206]) by esa-jnhn-pri.mail.uoguelph.ca with ESMTP; 29 Mar 2012 16:11:54 -0400 Received: from zcs3.mail.uoguelph.ca (localhost.localdomain [127.0.0.1]) by zcs3.mail.uoguelph.ca (Postfix) with ESMTP id 187E6B407B; Thu, 29 Mar 2012 16:11:54 -0400 (EDT) Date: Thu, 29 Mar 2012 16:11:54 -0400 (EDT) From: Rick Macklem To: Bob Friesenhahn Message-ID: <2042316157.1946865.1333051914085.JavaMail.root@erie.cs.uoguelph.ca> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [172.17.91.202] X-Mailer: Zimbra 6.0.10_GA_2692 (ZimbraWebClient - IE8 (Win)/6.0.10_GA_2692) Cc: freebsd-fs@freebsd.org Subject: Re: NFSv3, ZFS, 10GE performance 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: Thu, 29 Mar 2012 20:13:03 -0000 Bob Friesenhahn wrote: > On Wed, 28 Mar 2012, Rick Macklem wrote: > >> > >> Hopefully, readahead doesn't kill performance for smaller files.. > >> :-) > >> > > Well, readaheads only happen if the file is large enough for the > > readahead > > to be before EOF. As such, they just won't happen for small files. > > The real problem is for applications which do a seek and a new read > prior to consuming all the data which is being read ahead on its > behalf. This results in read amplification and increased latency for > the next seek+read. > Yes, random reads on a large file is a problem, as you noted before. (I was just clarifying the "small file" case and it's good that you are clarifying the "large file, non-sequential" case.) As jhb@ noted, disabling read-ahead may be a good idea for the POSIX hint. Thanks, rick > Bob > -- > Bob Friesenhahn > bfriesen@simple.dallas.tx.us, > http://www.simplesystems.org/users/bfriesen/ > GraphicsMagick Maintainer, http://www.GraphicsMagick.org/