Date: Fri, 23 Jan 2004 09:35:54 -0800 (PST) From: Doug White <dwhite@gumbysoft.com> To: Scott Mitchell <scott+freebsd@fishballoon.org> Cc: freebsd-current@FreeBSD.org Subject: Re: vn vs. md - persistent swap-backed memory disk? Message-ID: <20040123093004.Y60312@carver.gumbysoft.com> In-Reply-To: <20040119222601.GB572@tuatara.fishballoon.org> References: <20040119222601.GB572@tuatara.fishballoon.org>
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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
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