LVM (Logical Volume Manager) Concept on Linux RHEL / CentOS 5&6

L.V.M(Logical Volume Manager)

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

:8e    (Linux LVM)
:w   (save & exit)
#partx -a /dev/sda (update kernel)


To convert LVM partitions as physical volumes
#pvcreate /dev/sda
ex: pvcreate /dev/sda{9,10,11}

To view physical volumes
#pvdisplay

To create volume group
#vgcreate
ex: vgcreate bsrtech /dev/sda{9,10,11}

To view volume groups
#vgdisplay

To create a logical volume
#lvcreate -L <+size> -n
ex: lvcreate -L +300M /dev/bsrtech -n lv1

To view logical volumes
#lvdisplay

To format logical volumes
#mkfs.ext4 /dev/bsrtech/lv1

Create a mountpoint and mount logical volume on it
#mkdir /mysql
#mount  /dev/bsrtech/lv1   /mysql
#cd /mysql
 
To extend size of logical volume 
#umount
#lvresize -L +
ex:lvresize -L +200M  /dev/bsrtech/lv1
To make filesystem for extended size
#resize2fs
ex: resize2fs  /dev/bsrtech/lv1
 #mount /dev/bsrtech/lv1  /mysql
 
To reduce a logical volume
note: whenever we are reducing an LVM we have to take backup (More Details #man lvreduce)
#mkdir  /lvm-bkp
#cp -rf /mysql/*  /lvm-bkp

#lvreduce -L <-size>
ex: lvreduce -L -100M  /dev/bsrtech/lv1
 To format LVM
#mkfs.ext4
ex:mkfs.ext4 /dev/bsrtech/lv1

#mount /dev/bsrtech/lv1  /mysql
#cp -rf /lvm-bkp/* /mysql

To remove an LVM
#umount
#lvremove
ex:lvremove /dev/bsrtech/lv1

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

#vgextend
ex:vgextend /dev/bsrtech  /dev/sda12

To reduce volume group
#vgreduce
ex:vgreduce /dev/bsrtech  /dev/sda12


To remove volume group
#vgremove
ex:vgremove /dev/bsrtech

To delete physical volumes
#pvremove
ex:pvremove /dev/sda{9,10,11,12}