07-06-2012
Volume Group = An administrative group of Logical Volumes. A commercial computer can (and usually does) have multiple Volume Groups.
The sum of the size of alll the Volume Groups would be the total size of all the formatted disc space controlled by LVM.
You don't have to give all your discs up to LVM control, but there is rarely a reason to not give up all your Physical Volumes to LVM control.
Conventionally VG00 (Volume Group zero) is the system Volume Group (e.g. Logical Volumes: root, /usr, /var, /opt, /tmp ... and sometimes /home. No system account such as the root account should have its home directory on /home).
How you group your volumes after that is personal preference. I tend to use VG01 for user home directories and data, and VG02 onwards for databases. This is not a rule, just personal preference.
The Volume Groups become very important when designing backup strategies.
Physical Volume = From the point of view of your computer a physical hard disc.
Logical Volume = A logical disc which may spread across multiple physical discs. Your unix system will mount a Logical Volume on a mountpoint just as if it was a physical disc partition.
Hope this helps.
Last edited by methyl; 07-06-2012 at 05:22 PM..
Reason: typos, layout and formatting
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LEARN ABOUT FREEBSD
lvscan
LVSCAN(8) System Manager's Manual LVSCAN(8)
NAME
lvscan - scan (all disks) for Logical Volumes
SYNOPSIS
lvscan [-a|--all] [-b|--blockdevice] [-d|--debug] [-h|--help] [--ignorelockingfailure] [-P|--partial] [-v|--verbose]
DESCRIPTION
lvscan scans all known volume groups or all supported LVM block devices in the system for defined Logical Volumes. The output consists of
one line for each Logical Volume indicating whether or not it is active, a snapshot or origin, the size of the device and its allocation
policy. Use lvs(8) or lvdisplay(8) to obtain more-comprehensive information about the Logical Volumes.
OPTIONS
See lvm for common options.
--all Include information in the output about internal Logical Volumes that are components of normally-accessible Logical Volumes, such as
mirrors, but which are not independently accessible (e.g. not mountable). For example, after creating a mirror using 'lvcreate -m1
--mirrorlog disk', this option will reveal three internal Logical Volumes, with suffixes mimage_0, mimage_1, and mlog.
-b, --blockdevice
This option is now ignored. Instead, use lvs(8) or lvdisplay(8) to obtain the device number.
SEE ALSO
lvm(8), lvcreate(8), lvdisplay(8) lvs(8)
Sistina Software UK LVM TOOLS 2.02.95(2) (2012-03-06) LVSCAN(8)