Re: [linux-lvm] Total free space using added VGs and LVs

[Drew <drew.kay@gmail.com>]

> But I thought that the purpose of LVM was to make a number of partitions
> look like one big one. So I can understand that with an added volume group,
> the filsesystems are separate, but for my (2) below, I expected all LVM-type
> partitions to seen as one large one.

The purpose of LVM is to make a bunch of physical drives look like one
big pool of storage space. A Volume Group is a container into which
you plug physical volumes (drives) so that the logical volumes can
allocate space from the pool (volume group) as needed.

> 1) Why would you want several logical volumes in one volume group?

The same reason(s) you would want to partition a regular hard drive.

Maybe you only want /home to have 20GB so your kids can't flood the
computer with downloaded music. Maybe you want /var/www to have
restricted permissions so your home web server is less vulnerable to
hackers. Maybe you're running a PVR application like MythTV and want a
high-performance filesystem like XFS for storing recorded shows.

All of these can be done with logical volumes, and are often easier under LVM.


> 2) Why would you want several volume groups at all?

You don't need multiple volume groups on a single machine. There are
certain uses though in which it is beneficial, usually in commercial
use.


-- 
Drew

"Nothing in life is to be feared. It is only to be understood."
--Marie Curie