From owner-freebsd-current@FreeBSD.ORG Fri Jan 23 09:35:55 2004 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 8DFB416A4CE for ; Fri, 23 Jan 2004 09:35:55 -0800 (PST) Received: from carver.gumbysoft.com (carver.gumbysoft.com [66.220.23.50]) by mx1.FreeBSD.org (Postfix) with ESMTP id A7D0243D3F for ; Fri, 23 Jan 2004 09:35:54 -0800 (PST) (envelope-from dwhite@gumbysoft.com) Received: by carver.gumbysoft.com (Postfix, from userid 1000) id 9A0D872DC9; Fri, 23 Jan 2004 09:35:54 -0800 (PST) Received: from localhost (localhost [127.0.0.1]) by carver.gumbysoft.com (Postfix) with ESMTP id 9723D72DC7; Fri, 23 Jan 2004 09:35:54 -0800 (PST) Date: Fri, 23 Jan 2004 09:35:54 -0800 (PST) From: Doug White To: Scott Mitchell In-Reply-To: <20040119222601.GB572@tuatara.fishballoon.org> Message-ID: <20040123093004.Y60312@carver.gumbysoft.com> References: <20040119222601.GB572@tuatara.fishballoon.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII cc: freebsd-current@FreeBSD.org Subject: Re: vn vs. md - persistent swap-backed memory disk? X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 23 Jan 2004 17:35:55 -0000 On Mon, 19 Jan 2004, Scott Mitchell wrote: > Hi all, > > On 4.whatever, I can create a swap-backed vn(4) disk that will survive a > reboot, following the recipe in the vnconfig manpage. All very useful for > stuff in /tmp that I don't _really_ care about, but it's nice to have hang > around anyway. This is a peculiarity of how vn allocated swap fopr its use vs. md, probably. md works on a much higher level than vn, so it probably gets a random smattering of swap blocks when vn was allocating from the front or something like that. Needless to say a crashdump to that swap partition would eat it anyway, and its also possible that a crash would end up with a dirty or destroyed filesystem which would potentially abort the boot. That would be pretty embarrasing if your boot died because your /tmp rescue trick tried to rescue a badly corrupted FS. :) md also has tome tricks regarinding not creating blocks until they're actually written to, and reserve may be a noop. :) -- Doug White | FreeBSD: The Power to Serve dwhite@gumbysoft.com | www.FreeBSD.org