What is LOGICAL VOLUME MANAGEMENT?

In LVM we can merge many hard drives & make it as a single hard drive. In previous we cannot resize the file system. Also we have some partition limit in rhel 5 and 6.
If you make a hard drive of 10G using simple partition technique and somehow your drive get full so here we cannot expand it or reduce it. So we use LVM to get those advantages of reducing and expanding drives.
lvm2
Here we create 8 physical volume and using it we generate 1 Volume Group 1 TB. And we use 700G to create three logical volume and there is 300G remains in VG. The first LV get full so we use remaining 300G to extend that LV so such a way we can create LV and use it.
LVM
Here,
PV-> Physical volume
VG-> Volume Group
LV -> Logical Volume

Configure LVM (Logical Volume Management) Disc Management on CentOS/RHEL/Scentific Linux/Oracle Linux 7/6/5

Step-I (Make new partition)
[root@techbrown]# fdisk  /dev/sda

n:
e extended
p primary partition (1-4)
Make extended partition and then create partition using it.
First cylinder:
second cylinder :+5G
Create 3 more partition like this.

Then toggle it. To toggle type t
t: (x) (y) (z)  (8e)
:p:
:w
[root@techbrown]# partx   -a   /dev/sda
[root@techbrown]# pvcreate   /dev/sdax

OR

[root@techbrown]# pvcreate  /dev/sdax   /dev/sday   /dev/sdaz
Now create physical volume to create it
[root@techbrown]# pvdisplay

Or

[root@techbrown]# pvs  /dev/sdax

Now create VG.

Step-II (Vgcreate vgname pvname(list))
[root@techbrown]# vgcreate   myvol   /dev/sdax  /dev/sday  /dev/sdaz
[root@techbrown]# vgdisplay

OR

[root@techbrown]# vgs myvol

Lvm3

Step-III (Now create Logical Volume)

lvcreate -L lvsize -n Lvname vgname

[root@techbrown]# lvcreate  -L  2G  -n  lv1  myvol
[root@techbrown]# lvdisplay

Now Assign file system.

[root@techbrown]# mkfs.ext4  /dev/myvol/lv1
[root@techbrown]# mkdir /data
[root@techbrown]# vim /etc/fstab
/dev/myvol/lv1    /data    ext4   defaults   0    0
:wq
[root@techbrown]# mount    –a
[root@techbrown]# df   -hT
Step-IV (Remove LVM partition)
[root@techbrown]# umount   /data
[root@techbrown]# vim /etc/fstab
Remove entry
[root@techbrown]# lvremove   /dev/myvol/lv1
Step-V (For to remove VG)

First remove all active LVM then remove VG.

[root@techbrown]# vgremove   myvol
[root@techbrown]# pvremove  /dev/sdax   /dev/sday   /dev/sdaz
[root@techbrown]# fdisk  /dev/sda

Delete all Partition.

Step-VI (Create swap LVM)
[root@techbrown]# lvcreate   -L  +2G  -n   lv2   myvol
[root@techbrown]# mkswap  /dev/myvol/lv2
[root@techbrown]# vim   /etc/fstab
/dev/myvol/lv2     swap    swap    default    0    0
:wq
[root@techbrown]#swapon    -a
[root@techbrown]# cat /proc/swaps
Step-VII (To remove swap)
[root@techbrown]# swapof  -a
Step-VIII (Extend LV)
[root@techbrown]# vgs   myvol

Spaces are remaining then extend LV.

[root@techbrown]# lvextend   -L   +5G   /dev/myvol/lv1
[root@techbrown]#resize2fs   /dev/myvol/lv1
Step-IX (Reduce LV)
-Cannot reduce LVM partition on online mode
 -Only free space can reduce
[root@techbrown]# umount   /data
[root@techbrown]# df  -hT
[root@techbrown]# fsck.ext4   -f   /dev/myvol/lv1
Step-X (resize2fs LVname targated size)
[root@techbrown]# resize2fs   /dev/myvol/lv1   7G

lvreduce -L size (targeted size) LVname

[root@techbrown]# lvreduce -L 7G  /dev/myvol/lv1
[root@techbrown]# mount   -a
[root@techbrown]#  df   -hT
Step-XI (Using Physical extent and logical extent)
[root@techbrown]# vgcreate  -s  8G  myvol   /dev/sdax
[root@techbrown]#  lvcreate   -l   20   -n   lv3  myvol.

LVM4
Congratulations LVM is now Configured.