I'am using lvm since two years. Does snapshots on an irregular basis .

But I wanted to explore more ::

The following command converts the linear logical volume vg00/lvol1 to a mirrored logical volume.
lvconvert -m1 vg00/lvol1

The following command converts the mirrored logical volume vg00/lvol1 to a linear logical volume, removing the mirror leg.
lvconvert -m0 vg00/lvol1

I do not understand what is happening in the above command.

Which LV are being converted here?

The first command creates a two logical volumes where one is the mirror of the other logical volume.

But which mirrored logical volume is being converted into a linear LV.

I'm not certain if we really understand your questions.
The LV in this example is just what you would think: lvol1 in Volume Group vg00.

In the example, vg00/lvol1 is the equivalent of block device /dev/mapper/vg00-lvol1, /dev/vg00/lvol1 and a dm device /dev/dm-<something>.

In the '-m1' example and '-m0' examples, it is once again, vg00/lvol1. I think, unless you specify a Physical Volume 'lvconvert' will pick a suitable volume for you when you add a mirror; and will release the space on that volume when you take away a mirror (leaving your original linear LV). Unfortunately I have no way of testing this, so this is speculation.

My suspicion is that mirroring is not a popular, well understood or well used feature of LVM.

The quotes are from man pages.

That's the commands that I'm not understanding.

This page draws a picture of a mirror, http://www.centos.org/docs/5/html/Cl...d_volumes.html

Basically,
takes /dev/mapper/vg00-lvol1 and creates a mirror of it on another drive. Data is written to both the original filesystem and the mirrored copy of it. It is RAID1-like, but not really RAID. This page, http://www.centos.org/docs/5/html/Cl...orrecover.html, describes Recovering from LVM Mirror Failure in detail.

simply reverses the process and removes the mirror of /dev/mapper/vg00-lvol1, turning it back into a linear LV.

Does that help?