LVM (Logical Volume Manager) Concept on Linux RHEL / CentOS

 LVM is a method of allocating harddrive space into logical  volumes that can be easily resized instead of partitions.
 With LVM the harddrive (or) set of harddrives are allocated to  one or more physical volumes.
 The physical volumes are combined into volume  groups
 Each volume group is divided into logical volumes which are  assigned mountpoints such as /home and filesystem types such  as   ext3.
To configure LVM

1)Create three LVM partitions
2)Convert them as physical volumes
3)Create volume groups from physical volumes
4)Create logical volumes from volume groups and assign mountpoints

IMPLEMENTATION:
# fdisk /dev/sda
n
+500M
t
<partition number>
8e
w
partprobe
To convert LVM partitions as physical volumes
# pvcreate /dev/sda<partition numbers>
ex: pvcreate /dev/sda{9,10,11}

To view physical volumes
# pvdisplay

To create volume group
# vgcreate <vg name> <partitions>
ex: vgcreate maaza /dev/sda{9,10,11}

To view volume groups
# vgdisplay

To create a logical volume
# lvcreate -L <+size> <vg name> -n <LV name>
ex: lvcreate -L +500M /dev/maaza -n fanta

To view logical volumes
# lvdisplay

To format logical volumes
# mke2fs -j /dev/maaza/fanta

Create a mountpoint and mount logical volume on it
# mkdir /cyber
# mount /dev/maaza/fanta /cyber
# cd /cyber

To extend size of logical volume
# umount <mountpoint>
# lvcreate -L <size> <lv name>
ex:lvcreate -L +500M /dev/maaza/fanta

To make filesystem for extended size
# resize2fs <logical volume>
ex: resize2fs /dev/maaza/fanta
# mount /dev/maaza/fanta /cyber

To resize a logical volume
note:whenever we are reducing an LVM we have to take backup
# mkdir /a
# cp -rf /cyber/* /a

# lvreduce -L <-size> <LVM>
ex: lvreduce -L -100M /dev/maaza/fanta

To format LVM
# mkfs.ext3 <logical volume>
ex:mkfs.ext3 /dev/maaza/fanta

# mount /dev/maaza/fanta /cyber
# cp -rf /a/* /cyber

To remove an LVM
# umount <mountpoint>
# lvremove <logical volume>
ex:lvremove /dev/maaza/fanta

To extend volume group
1)create another LVM partition
2)convert into physical volume

# vgextend <vg name> <partition name>
ex:vgextend /dev/maaza /dev/sda12

To reduce volume group
# vgreduce <vgname> <partition name>
ex:vgreduce /dev/maaza /dev/sda12

To remove volume group
# vgremove <vg name>
ex:vgremove /dev/maaza

To delete physical volumes
# pvremove <partitions>

ex:pvremove /dev/sda{9,10,11,12}