Quoting from the LVM2 Resource Page:
LVM2 refers to a new userspace toolset that provide logical volume management facilities on linux. It is reasonably backwards-compatible with the original LVM toolset. To use LVM2 you need 3 things: device-mapper in your kernel, the userspace device-mapper support library (libdevmapper) and the userspace LVM2 tools.
The following tries to describe LVM, roughly:
[sda]---[sdb] [sdc]---[sdd] ← LVM physical volume (pv) | -----|----- | | ---[vg] --[vg]---.... ← LVM volume group | | | | | [lv] [lv] [lv] [lv] [lv] ← LVM logical volume
Volumes are not activated
If logical volumes (and/or volume groups and/or physical volumes) are not visible via lvs, vgs, pvs, chances are that the logical volumes are in place, but inactive and not present in /dev/mapper. To activate all volumes, try this:
for v in `lvs -o vg_name,name --noheadings --separator /`; do echo "V: $v" lvchange -ay /dev/"$v" done
Now the volumes should show up in /dev/mapper.