I have a system with CentOS V5.3 and a 30GB HDD with 21 GB free on it.
I added a 40 GB HDD with a single ext3 partition with no data on it, but free space remains at 21 GB.

OK, I read a number of posts from a few years ago, but none are quite clear to me. So I edited my original post to ask the following:

1) On the added HDD, I created a single partition of type ext3 with GParted. Was this the right thing to do? I did not format it, as I didn't think it was needed in Linux.

2) After the HDD is partitioned, can the rest be done using LVM alone, or are there some steps that must be done via a terminal window command line and/or modifying fstab.

3) If more than LVM is needed, what are the steps before and/or after fstab. It would be nice to have this single partition HDD visible as a separate folder in Linux.

Regards,
Lou.

1) You would have had to format it to create an ext3 partition.
2) Depends what 'the rest' is. In general, you will need to mount a drive to make use of it, normally through adding it to /etc/fstab
3) If you just want to mount the HDD to a directory, you don't need any of LVM. You just format the drive and mount it wherever you need it.

So, in general, you'd be directed to:
1) Partition and format the drive as you wish (generally ext3 partition(s))
2) Create the directory under which you want to mount the drive
3) Add the drive to /etc/fstab (there's a gazillion howto's on the net)
4) Mount the drive

But since you've mentioned LVM I've a feeling you're after more than this, though I don't know what.

First, I understood all your instructions. But LVM is supposed to treat the added drive as a seemless part of the disk space. (Does just mounting the drive do that also?)

But under LVM, I wanted to add the new space under a separate Volume Group and Logical Volume. Then how can I see the contiguous total amount?

The thing is: If I add the disk to the existing group, then I cannot remove it without corrupting the filesystem. I hope that creating a separate group will allow me to later delete the group and replace the drive without destroying filesystem.

Well, I'm stumped.

I created an additional volume group VolGrp40GBHDD, and logical volume LogVol40GBHDD to represent the HDD and created the full amount of extents for that logical volume.

But the native file browser only sees the free space from the OS drive and none of the space on the new drive.
How do I get the OS to see the new drive's space without adding the drive to the existing Volume group (of the OS's drive)?

LVM is used to make "virtual partitions" (called "logical volumes", LVs) which you then make file systems in and mount them in the same way you would with real partitions. AFAIK "native file browser"s (what are you using?) browse files-and-directories on mounted file systems; they do not browse partitions.

I'm using CentOS, and its native file browser. Under the right selection, that browser shows the total free space available (status bar, bottom-left)to the system over all partitions. (I have verified this experimentally.)

I just had a self-administered crash course in LVM, so I know what a volume group and a logical volume is. The point behind LVM is to make all disk space seem contiguous to the OS.

What I don't understand is why adding the new HDD (with a single partition) to a new Logical Volume within a new volume group, does not produce the same result as adding the drive to an existing Logical volume in an existing volume group?