From owner-freebsd-fs@FreeBSD.ORG Wed Feb 6 07:22:11 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 26F0A16A420 for ; Wed, 6 Feb 2008 07:22:11 +0000 (UTC) (envelope-from bsd@fluffles.net) Received: from mail.fluffles.net (fluffles.net [80.69.95.190]) by mx1.freebsd.org (Postfix) with ESMTP id 04D0013C465 for ; Wed, 6 Feb 2008 07:22:10 +0000 (UTC) (envelope-from bsd@fluffles.net) Received: from [10.0.0.18] (cust.95.160.adsl.cistron.nl [195.64.95.160]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: info@fluffles.net) by mail.fluffles.net (Postfix) with ESMTP id 9937AB29D5D for ; Wed, 6 Feb 2008 08:01:43 +0100 (CET) Message-ID: <47A95BC0.1060307@fluffles.net> Date: Wed, 06 Feb 2008 08:03:28 +0100 From: "fluffles.net" User-Agent: Thunderbird 2.0.0.6 (X11/20071022) MIME-Version: 1.0 To: freebsd-fs@FreeBSD.org Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Cc: Subject: delayed write buffer 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: Wed, 06 Feb 2008 07:22:11 -0000 Hello kind list, I was wondering how to tune FreeBSD's VFS write buffer. I would like a large amount of RAM (say 500MB out of 1GB) to be reserved or allocated to be used as write buffer for my backup NAS system. If i understand the mechanism correctly, a "dd if=/dev/zero of=/mnt/fs bs=1m count=500" would act as if i used a malloc-backed md device. This leads to very nice performance gains, especially in my case because i'm using encryption causing throughput to be limited to 22MB/s. But if the first 500MB is free, i can mask this limitation and experience a fast drive, when writing that is. Anyone can point me to the right directions? I tried playing with some sysctl vfs (notably the vfs.maxmallocbufspace tunable) but did not achieve the desired effect. And yes, i do know a lot of dirty buffers is dangerous but my storage setup is redundant enough. Besides i'm just curious in this topic. :) Could a regular BIO-FLUSH caused by UFS metadata sync be the curlpit? Thanks for any assistance! Kind greetings, Veronica