[PLUG] Odd partition has appeared

[Dale Snell]

On Sat, 06 Nov 2010 15:28:34 -0700
John Jason Jordan <johnxj at comcast.net> wrote:

> Following my recent upgrade from Fedora 11 x86_64 to Fedora 13
> x86_64, I have discovered that there is now a new partition
> listed by Nautilus when I view the "Computer" folder. It now
> lists:
> 
> CD/DVD Drive
> vg_devil8
> File System
> 
> "Devil8" is the name of the computer, so that part is clear.
> The icon for vg_devil8 looks like an older, taller hard drive.
> It has a round green blob in the corner that says VG in tiny
> white letters. If I double click on vg_Devil8 Nautilus gives me
> an error message that it can't mount the location.
> 
> Also, there is now a menu item Under System > Administration
> labeled Logical Volume Manager. Launching it gives me a GUI
> view of vg_devil8, where "vg" apparently stands for "volume
> group." The GUI shows a "logical view" and a "physical view" of
> sda2, the root partition. (I set up the 320 GB hard drive with
> a 200 MB boot partition, and the remainder as sda2 for root; no
> separate swap partition.)

John,

A "logical volume" (LV) is a block of storage, the characteristics
of which are maintained by the OS, rather than by the disk drive.
There are a number of advantages to using logical partitions.

* Unlike a disk partition, which is limited to a single drive, an
LV can contain multiple partitions, from multiple drives.  This
means that you can have a whopping big "partition" without having
to spend the money on a whopping big drive.

*  Partitions can be re-sized in an LV fairly easily.  You can
have a large LV, and a number of small partitions with unused
space in the LV.  If you need to enlarge a partition, it's
reasonably easy, and you don't have to mess with the underlying
hard drive partitioning.  You can also easily add a partition to
the LV.

*  You can add more physical volumes (read: hard drive partitions)
to an existing LV.  I haven't done this, but from what I've read,
it doesn't look very difficult.

*  It is possible to "snapshot" an LV, for backup purposes.  I
have not looked into this, so I don't know how it works.  However,
it looks like it should be a nice way of being able to run full
backups of a live system.

The graphical tool you mentioned is pretty nice -- certainly
easier than doing it via the command line.  My oh my is there a
lot of typing involved.  It's not hard, but don't make any
mistakes.  (I've used both methods.  Trust me, the GUI's easier!)

The use of LVs has been an option since Fedora 10, I think.  With
F12, it became the default, and you had to explicitly turn it off
if you didn't want to use it.  I'd resisted using it up to F12,
but finally decided to try it.  It works, I'm happy, and I doubt
that I'll go back to the old way.  Granted, it's fiddly-er to use
than standard partitioning, but it has its advantages.

> All seems to be fine except that gParted now shows /dev/sda2
> with a big orange triangle with an exclamation mark in it and
> the file system is now lvm2, where it used to be labeled ext3.
> Right clicking on /dev/sda2 and selecting Information gives a
> warning "Logical volume management is not yet supported." I
> assume that warning means that gParted doesn't support it,
> since everything seems to be running fine.

Doesn't work in F13, eh?  Hmpf.  I'm going to upgrade to F14 here
soon.  Maybe it'll be working there.  OTOH, the GUI logical volume
manager does work, so maybe there's no hurry.

> I suppose now I'm going to have to spend hours googling to
> figure out what a logical volume is as opposed to a partition,
> and why Fedora 13 decided I needed one.

I _think_ there's an explanation in the Release Notes.  If not,
some of the other docs on the Fedora Project web site should have
the information you want.  <http://fedoraproject.org>

Anyway, you shouldn't have any trouble with the LV setup.  Hope
this helped.

--Dale

--
Q:  How many IBM CPUs does it take to execute a job?
A:  Four; three to hold it down, and one to rip its head off.