From owner-freebsd-questions  Wed Mar 21 19:16:16 2001
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From: Mike Meyer <mwm@mired.org>
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Date: Wed, 21 Mar 2001 21:16:12 -0600
To: Eric M Logan <ericmlogan@mediaone.net>
Cc: questions@freebsd.org
Subject: Re: ramdisks and mfs...
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Eric M Logan <ericmlogan@mediaone.net> types:
>     Is there a difference between /dev/md* and mounting a partition from
> swap.  Let me elaborate.  I have a swap partition mounted and I have
> /tmp mounted using the same address as that swap partition.  Anything I
> put in /tmp will therefore be gone upon reboot.  Is this what's
> considered a ramdisk in Freebsd?  Or, is using /dev/md* mounted
> somewhere what's known as a ramdisk in FreeBSD?  In Linux, it's the
> latter.  Any help would be appreciated, thanks.

I assume you're using mfs for /tmp. Yes, that qualifies as a ramdisk,
even though it's backed by swap. If you don't need the memory back,
it'll act just like a ramdisk. If you do need the memory for something
else, your data will be paged out to swap, and have to be read back
from disk. md isn't backed by swap, so the data is always in ram,
meaning the memory isn't usable by anything else.

	<mike
--
Mike Meyer <mwm@mired.org>			http://www.mired.org/home/mwm/
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.

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