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From: Lowell Gilbert <freebsd-questions-local@be-well.ilk.org>
To: clutton <clutton@zoho.com>
Subject: Re: FreeBSD working from RAM (MFSROOT) as a Workstation.
References: <1417734458.1772.1.camel@zoho.com>
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Date: Fri, 05 Dec 2014 00:08:56 -0500
In-Reply-To: <1417734458.1772.1.camel@zoho.com> (clutton@zoho.com's message of
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clutton <clutton@zoho.com> writes:

> Is anyone use a FreeBSD as a Desktop working from RAM, using MFSROOT?

That only speeds up the *first* load of each memory page mirroring a
disk sector. After the system has been up a while, it's actually slower
than running with a disk, because everything you actually use will have
two copies in RAM: one on the disk image, and the one that's actually
occupying normal resident pages.

Furthermore, you have to load your whole root filesystem from disk
before you start, even the parts you haven't used yet. I would expect
that to give you a *slower* startup time. RAM is faster than SSD access,
but the SSD is non-volatile, whereas the RAM needs to be repopulated
from non-volatile storage every time you boot. And every page that is
used has to get loaded into the RAM disk and *then* loaded into virtual
memory.

TL;DR: To run from RAM, you first have to load the RAM. The chances that
an MFSROOT does this more efficiently (than starting directly from the
nonvolatile disk) seem remote.