What is this LVM thing and how do I use it?

LVM stands for Logical Volume Manager. It is the standard way of managing disks and partitions since eCS 1.0.

With LVM the user can:

• assign drive letters the way he/she prefers
• make eCS "see" foreign partitions even if/when there's no native IFS driver (this means that you can assign a drive letter to the partition, not that you can actually READ its contents. Why should you want to do it? For example you may want to keep the same drive lettering across multiple OSes)
• make a single JFS volume spanning more than one physical disk
• extend a JFS volume by adding another physical disk

With LVM you have to distinguish among partitions and volumes.

In an LVMized eCS everything on disk is a volume: there are no more partitions. Volumes are the native unit of work for LVM.

You can use HPFS, FAT or JFS to format a native volume. The only file system that can be extended btw is JFS.

If you want to access partitions created with legacy FDISK or by other OSes you have to create a "compatibility volume" and assign the old partition to it.
With LVM you can also create old-styled partitions, but then you need to assign them to a compatibility volume to be able to use them correctly (e.g. you need it to create bootable volumes).

If you want to have access to all the advanced features of JFS and LVM (jounaling file system, disk spanning, etc.) you should create an "LVM volume", that is a native volume. Then format it with JFS.

The "LVM" utility included in eCS (either the text-based or the graophcal one) is powerful, and is the only one that can harness all the power of LVM. But if you're accustomed to the classical "FDISK" approach, the LVM utility can be quite confusing.
Recent eCS releases (from 1.2 onward I believe) include the MiniLVM tool which is much easier to use for most common tasks.
You can find it in the "System Setup" folder. It is titled "Maintenance & Installation Volume Manager".

If you want to use the more complete LVM utility you can find it in the "Programs" -> "Utilities" folder, under the name "Logical Volume Manager (Advanced)". Or you can go to the "Local System" -> "Drives" folder, right click, and choose "Manage Volumes" from the popup menu.
You'll find a lot of information on LVM by using the included online help.