Re: Disk Volumes Question

In article <2006081113100116807-raggionospam@optonlinenet>,
raggio <raggio.nospam@xxxxxxxxxxxxx> wrote:

Hi all. First of all I am a Unix and OS X newbie. I am a Windows
convert to a Mac mini. Sorry in advance for the length of the message.
I appreciate your time in reading this and offering a suggestion.

Here's my question. It is related to another post I made about
deleting an OS X install from an external drive. To do the hacking I
used Terminal (sudo bash), scary stuff. Anyway when I listed the
contents /Volumes, I find the following:

mini:/Volumes raggio$ ls -al
total 40
drwxrwxrwt 8 root admin 272 Aug 11 12:02 .
drwxrwxr-t 34 root admin 1258 Aug 11 11:54 ..
-rw-rw-rw- 1 frank admin 6148 Feb 4 2006 .DS_Store
-rwxrwxrwx 1 raggio raggio 82 Jan 25 2006 ._RAGGIO NANO
-rwxrwxrwx 1 samantha samantha 82 Apr 29 11:09 ._RAGGIO SHUF
drwxrwxrwx 3 raggio admin 102 Feb 4 2006 Extern120
drwxrwxr-t 18 root admin 714 Aug 11 02:51 Extern120 1
lrwxr-xr-x 1 root admin 1 Aug 11 11:55 Macintosh HD -> /
mini:/Volumes raggio$

I see my two iPods that I dock as well as three HD. The problem is
that I only have 2 HD. "Extern120" is sort of listed twice. The one
"Extern120 1" is the one that actually contains my files. According to
Disk Utility that is the mount point for the HD. What is the entry
"Extern120" then? Can it be deleted? It has some files in it, but I
see no way to reach it via Finder etc. I think it is a volume left
over from when I first configured the HD to use USB instead of Firewire
in my external enclosure. It looks like it only has a previous version
of an iPhoto DB. The dates are all from Feb. which is when I got the
Mac It looks like the iPhoto DB on "Extern120 1" is more current and
complete.

1) Should I delete "Extern120"? How to do it? I want to make sure
that "Extern120 1" does not somehow actually reference "Extern120" and
that it can be deleted. I'd love to have the 18 GB back and nobody
likes junk on their drive.

2) Where can I find out more about Volumes in general an specifically in OS X?

3) How do you think this happened? Is it normal for an external
enclosure to create different mount points for USB and Firwire? That
is just a theory, BTW.

4) Can I rename "Extern120 1" to "Extern120" once I delete the old one?
I hate having a space in the name, but not a big deal.

More than anything I'm just trying to learn more about the system.

Thanks,
John

Some generic mounting information UNIX vs Windows

UNIX mounts volumes on top of a directory so that the new volume
is in the in the single UNIX file name space.

UNIX doesn't care what directory you mount the volume on, however
there are conventions. Mac OS X has the convention of creating
an empty directory based on the volume name in /Volumes and then
mounting the volume there. Other UNIX system use different
conventions.

NOTE: UNIX doesn't care if the directory is empty or not. After
the mount anything in a directory used as a mount point is hidden
until the mounted volume is unmounted.

And when you do unmount a volume on UNIX, generally the mount
point directory is left behind. Of course it all depends on
whether you are dealing with the UNIX side of the house or the Mac
OS X GUI side of the house. When you tell the Finder to unmount
the volume by ejecting it (or clicking on the triangle, or by
dragging the volume to the trash), then the Finder does a UNIX
unmount, and then it will delete the
/Volumes/mount_point_directory. However, if there is something in
that directory, it will leave it alone, which appears to be the
case for Extern120.

If you want to see which volume a specific directory is located on
from bash, then just do "df /path/to/the/directory". This will
tell you the mount point information for the volume holding that
directory.

In the Windows world you might think of a UNIX mount point as
being similar to D:, E:, F:, G:, etc..., except that in UNIX you
do not run out of letters because you can always create more
directories to act as mount points, and they don't have to live in
any specific location in the file name space. And in UNIX after
you have mounted the volume, any UNIX commands and utilities that
walk the directory tree do not need to do anything special to
include the newly mounted volume in their tree walk, because it
just looks like yet another directory in the name space. In fact
utilities that do not want to cross over to a different volume
when walking the name space, need to do something special to
determine that a directory is on a different volume from its
parent.

Another way to think about a UNIX mount point is that it is
kind-of similar to a Windows NTFS Reparse-Point (but not really).

I think NTFS gets real mount points in Vista, but to be very
truthful, I'm not that knowledgeable about Windows, so if any of
this doesn't makes sense, then assume I've got it wrong somehow.

If you want to know more about the UNIX side of Mac OS X (or the
GUI side for that matter), I would suggest spending some quality
time in a good bookstore drinking lots of over priced beverages in
the cafe while browsing through all the interesting Mac OS X
books. You should be able to find books about the Mac OS X GUI
and its Mac'ish features, books on Mac OS X's flavor of UNIX, as
well as one or 2 books for Windows to Mac switchers.

And if you want to continue with the UNIX side, then there are a
few books in the UNIX/Linux section of the computer books that
might be of interest, such as books on Bash and any other book
that seems interesting.

If you find a book that "Speaks to you", then buy it and read more
of it at home where the coffee is much cheaper :-)

Oh yea, and if you are really interested in digging deep (much
deeper than anyone needs to go), there is the new "Mac OS X
Internals: A Systems Approach" by Amit Singh. I'm almost up to
page 400, and I'm less than a quarter of the way through it :-)

Bob Harris
.

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