From owner-freebsd-fs@FreeBSD.ORG Sun Jan 26 03:01:59 2014 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 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 6BA1481F for ; Sun, 26 Jan 2014 03:01:59 +0000 (UTC) Received: from hergotha.csail.mit.edu (wollman-1-pt.tunnel.tserv4.nyc4.ipv6.he.net [IPv6:2001:470:1f06:ccb::2]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id 250B9109D for ; Sun, 26 Jan 2014 03:01:58 +0000 (UTC) Received: from hergotha.csail.mit.edu (localhost [127.0.0.1]) by hergotha.csail.mit.edu (8.14.7/8.14.7) with ESMTP id s0Q31s1K045572; Sat, 25 Jan 2014 22:01:54 -0500 (EST) (envelope-from wollman@hergotha.csail.mit.edu) Received: (from wollman@localhost) by hergotha.csail.mit.edu (8.14.7/8.14.4/Submit) id s0Q31rXu045569; Sat, 25 Jan 2014 22:01:53 -0500 (EST) (envelope-from wollman) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <21220.31393.533799.991163@hergotha.csail.mit.edu> Date: Sat, 25 Jan 2014 22:01:53 -0500 From: Garrett Wollman To: Matthew Ahrens Subject: Re: ZFS read performance anomaly / performance regression In-Reply-To: References: <21219.21690.165105.561362@hergotha.csail.mit.edu> X-Mailer: VM 7.17 under 21.4 (patch 22) "Instant Classic" XEmacs Lucid X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.4.3 (hergotha.csail.mit.edu [127.0.0.1]); Sat, 25 Jan 2014 22:01:54 -0500 (EST) X-Spam-Status: No, score=-1.0 required=5.0 tests=ALL_TRUSTED autolearn=disabled version=3.3.2 X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on hergotha.csail.mit.edu Cc: freebsd-fs 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: Sun, 26 Jan 2014 03:01:59 -0000 < said: > How are you reading the files? Could you be reading in less than > block-size chunks (default 128K)? Nope. dd bs=1024k. > This sounds similar to issue discussed in the thread with subject "ZFS slow > reads for unallocated blocks", which was comparing sparse vs cached reads. > Since your storage is so fast, prefetch will probably read and cache the > blocks by the time you issue the read() syscall, so you may be hitting a > similar issue. How would that have changed between 9.1 and 9.2? -GAWollman