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Newsgroups: alt.os.linux.ubuntu
From: Sybren Stuvel 
Subject: Re: Question about mount command and location of files
References:   <54pnb4F21pso3U1@mid.individual.net>

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Chris Fasano enlightened us with:
>
> Thank you.  This explanation is (somewhat) what's causing my
> misunderstanding.  If files aren't physically moved by mounting, then if I
> create a directory under hda1 (home/newdirectory) the /newdirectory is
> physically located on hda.
>
> So why would any files now created under /newdirectory be physically
> located on hdb just because I mounted /dev/hdb1 to /home/newdirectory,
> since as you say "mounting does not shift files physically?"

Let me try to explain. Let's assume that hda1 contains your root
filesystem, like this:

Filesystem:         Physical:
/                   /        on hda1
/etc                /etc     on hda1
/home               /home    on hda1
/usr                /usr     on hda1

Let's say you now mount hda2 on /home and you mkdir /home/somedir.
Your filesystem now looks like this:


Filesystem:         Physical:
/                   /        on hda1
/etc                /etc     on hda1
/home               /        on hda2
/home/somedir       /somedir on hda2
/usr                /usr     on hda1

Because you mounted hda2 on /home, the root of hda2 is available at
/home. Files in /home/somedir thus reside on hda2.

Still with me so far? I hope so.

If you unmount hda2, and re-mount it on /usr, your filesystem looks
like this:

Filesystem:         Physical:
/                   /        on hda1
/etc                /etc     on hda1
/home               /home    on hda1
/usr                /        on hda2
/usr/somedir        /somedir on hda2

The files in /home/somedir have now moved to /usr/somedir because of
the remounting. However, they are still in the same physical location,
/somedir on hda2. That is what's ment with "mounting does not shift
files physically".

Sybren
-- 
Sybren Stüvel
Stüvel IT - http://www.stuvel.eu/
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