From owner-freebsd-questions@FreeBSD.ORG Mon Jun 11 00:36:33 2012 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 14DB5106566C for ; Mon, 11 Jun 2012 00:36:33 +0000 (UTC) (envelope-from wblock@wonkity.com) Received: from wonkity.com (wonkity.com [67.158.26.137]) by mx1.freebsd.org (Postfix) with ESMTP id C2F158FC0C for ; Mon, 11 Jun 2012 00:36:32 +0000 (UTC) Received: from wonkity.com (localhost [127.0.0.1]) by wonkity.com (8.14.5/8.14.5) with ESMTP id q5B0aVCo079110; Sun, 10 Jun 2012 18:36:31 -0600 (MDT) (envelope-from wblock@wonkity.com) Received: from localhost (wblock@localhost) by wonkity.com (8.14.5/8.14.5/Submit) with ESMTP id q5B0aV0P079107; Sun, 10 Jun 2012 18:36:31 -0600 (MDT) (envelope-from wblock@wonkity.com) Date: Sun, 10 Jun 2012 18:36:31 -0600 (MDT) From: Warren Block To: Robert Huff In-Reply-To: <20437.14520.364554.528919@jerusalem.litteratus.org> Message-ID: References: <48774.1339367039@tristatelogic.com> <20437.14520.364554.528919@jerusalem.litteratus.org> User-Agent: Alpine 2.00 (BSF 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7 (wonkity.com [127.0.0.1]); Sun, 10 Jun 2012 18:36:31 -0600 (MDT) Cc: freebsd-questions@freebsd.org, "Ronald F. Guilmette" Subject: Re: Making a bootable backup (hard)disk... how? X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 11 Jun 2012 00:36:33 -0000 On Sun, 10 Jun 2012, Robert Huff wrote: > > Ronald F. Guilmette writes: > >> Warren? Just a couple more quick questions. You recommend: >> >> >> dump -C16 -b64 -0uanL -h0 -f - /usr | (cd /mnt && restore -ruf -) >> >> I'm real curious about you suggestions for the -C and -b values. >> >> I have what amounts to a personal workstation. Yea, OK, it is running >> mail, web, and FTP servers also, but fundementailly, it is not that busy >> most of the time. And it's got 4GB of main installed. On average, I >> suspect that I ain't even using half of that. >> >> Given all that, why shouldn't I specify (e.g.): -C512 -b1024 ? >> >> Wouldn't that all make the dump go faster? > > There are many possible obstacles to faster dump speed; > enumerating them is left as an exercise for the reader. > As it happens, I have a set-up very similar to what you > describe ... except with 8g of memory. A few years ago I did some > testing with various cache sizes (as part of diagnosing other > problems) and ended up with C=32. > (I should probably run the tests again, given some hardware > changes since.) > That machine's level 0 runs tonight; I will try to remember to > (retain and) post the results. -C16 is a little small because it's hard to tell how much memory someone running the example will have. I usually use -C32 on machines with plenty of memory. Remember that dump forks multiple times, so it's not 32M, but N*32M. -b64 is the largest safe buffer size to use. People have experienced problems with larger amounts.