man lvm: define LVM and its terms

The lvm(8) man page never said what LVM is,
it never defined what the acronym LVM stands for,
it never spelled out other common acronyms VG, PV, LV,
and never described what they are.

This adds a very minimal definition which at least defines
the acronyms and entities, but it could obviously be
expanded on, either here or elsewhere.

1 files changed, 14 insertions, 2 deletions

diff --git a/man/lvm.8_main b/man/lvm.8_main
index 31c4d7ee2..7506eaf60 100644
--- a/man/lvm.8_main
+++ b/man/lvm.8_main
@@ -11,8 +11,20 @@ lvm \(em LVM2 tools
 .
 .SH DESCRIPTION
 .
-lvm provides the command-line tools for LVM2.  A separate
-manual page describes each command in detail.
+
+The Logical Volume Manager (LVM) provides tools to create virtual block
+devices from physical devices.  Virtual devices may be easier to manage
+than physical devices, and can have capabilities beyond what the physical
+devices provide themselves.  A Volume Group (VG) is a collection of one or
+more physical devices, each called a Physical Volume (PV).  A Logical
+Volume (LV) is a virtual block device that can be used by the system or
+applications.  Each block of data in an LV is stored on one or more PV in
+the VG, according to algorithms implemented by Device Mapper (DM) in the
+kernel.
+.P
+
+The lvm command, and other commands listed below, are the command-line
+tools for LVM.  A separate manual page describes each command in detail.
 .P
 If \fBlvm\fP is invoked with no arguments it presents a readline prompt
 (assuming it was compiled with readline support).