From owner-freebsd-fs@FreeBSD.ORG Tue Jul 8 21:10:11 2008 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 529C71065677 for ; Tue, 8 Jul 2008 21:10:11 +0000 (UTC) (envelope-from kris@FreeBSD.org) Received: from weak.local (freefall.freebsd.org [IPv6:2001:4f8:fff6::28]) by mx1.freebsd.org (Postfix) with ESMTP id B6E798FC1B; Tue, 8 Jul 2008 21:10:08 +0000 (UTC) (envelope-from kris@FreeBSD.org) Message-ID: <4873D7B5.2060901@FreeBSD.org> Date: Tue, 08 Jul 2008 23:10:13 +0200 From: Kris Kennaway User-Agent: Thunderbird 2.0.0.14 (Macintosh/20080421) MIME-Version: 1.0 To: Ollivier Robert References: <20080708100701.57031cda@twoflower.in.publishing.hu> <4873C4FA.2020004@FreeBSD.org> <20080708204226.GB97977@keltia.freenix.fr> In-Reply-To: <20080708204226.GB97977@keltia.freenix.fr> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: freebsd-fs@freebsd.org Subject: Re: Thinking of using ZFS/FBSD for a backup system 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: Tue, 08 Jul 2008 21:10:11 -0000 Ollivier Robert wrote: > According to Kris Kennaway: >> (ports-i386:~)> cat /boot/loader.conf >> vfs.zfs.prefetch_disable=1 >> vm.kmem_size=1572864000 > > Hvae you tried w/o the prefetch_disable tunable? I have not done careful measurements, but casual observation suggests that on my workloads I get better performance without prefetch. I have a pair of mirrored disks on an amr, and my workload is quite random-access so prefetching just introduces latencies and wastes already-saturated disk bandwidth. With more disks or a different workload I would expect different performance characteristics. Kris