LVM : A good way to utilize disks space

Scenario :
Let say , You have 5 disks each with 20 GB , now you have requirements to create FS of size 25 GB and 35GB and let rest of the  space  unassigned for any future needs .
 Technically , this is  not possible to allocate space as each disk is only 20 GB in size and we can’t  use them for 25GB and 35GB partitions . So , we will use LVM(Logical Volume Manager) , merge all the disks in to one large pool ( volume group ) and then use space from that pool for further allocation . 
 LVM is  to serve requests where number  of  disks with small size can be put into a pool which can be further utilized to allocate space as per needs . Another advantage , if the pools is going to be full/packed then we can add additional disks ( pvcreate then vgextend following lvextend  ) later to increase the LVM  volume group size and Logical Volume sizes .
 
This merging will provide total space around 100 GB , out of that space we can allocate 60 GB ( 25GB+35GB) for our needs .
Logical Steps To create LVM Partitions :
Step:1  Create Physical volume 
This contains the number of disks which will be later merged to get a big size of disk in one pool.
# pvcreate   <disk-name>  <disk-name> 
Step:2  Create Volume group :
This is the name of the pool which have total amount  disks size which later be assigned to Logical volumes to create partitions of varying size .
# vgcreate   <volumegroupname>  <disks which needs to be part of this volume group name>
Step:3 Create  Logical Volume
# lvcreate -L <size for lvm>   -n  <lvmname>  <volume-groupname>  
The partition of this much size will be created in below mentioned way  :
/dev/vg_name/lv_name
You can now  format it with ext3/ext4 FS to make it writable and mountable .
Additional notes : You can rename VG and LV names easily  but make sure they are unmounted before you do these operations .
# vgrename   <old_vg_name>  <new_vg_name>
# lvrename  <vg_name>   <old_lv_name>   <new_lv_name>
We will keep posting for any additional docs on LVM .

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