Problem

The following describes the process of creating the three layers in the LVM architecture using an installation of RHEL/CentOS.

Notable

XFS file systems do not allow logical volume size reduction, which is used as the default on RHEL7.
By default vgcreate will automatically flag a physical volume that is doesn’t have a type associated with it (e.g. 8e for MBR or 8300 for GPT).

Solution

Layer 1: Physical Volume (PV)

Create a MBR or GPT partition.
Assign partition to PV.
```
 pvcreate /dev/${DEVICE}
```

Verify the PV.

 # Listing
 pvs

 # Summary
 pvdisplay

 # Hierarchical
 lsblk

Layer 2: Volume Group (VG)

Assign PV to VG.
```
 vgcreate ${VG_NAME} /dev/${DEVICE}
```
Verify the VG.
```
 # Listing
 vgs

 # Summary
 vgdisplay
```

Physical Extent (PE)

When creating a VG, a PE size is used. The PE size defines the size of the building blocks used to create logical volumes.

By default, the extent size is 4MiB. Also, the PE size is always specified as a multiple of 2MiB, with a maximum size of 128 MiB. Use the -s option to specify the PE size.

Logical Extent (LE)

When working with an Ext4 file system, a LE size is used. The LE size defines the size of the building blocks used to create logical volumes.

Notice the extent size on LVM is in no way related to the extent sizes that are used on the file systems.

Layer 3: Logical Volume (LV)

Assign LV to VG.

 # Absolue size
 lvcreate -n ${LV_NAME} -L 100M ${VG_NAME}

 # Relative size
 lvcreate -n ${LV_NAME} -l 50%FREE ${VG_NAME}

Verify the LV.

   # Listing
   lvs

   # Summary
   lvdisplay

Create a file system on top of the LV.
```
   mkfs.xfs /dev/${VG_NAME}/${LV_NAME}
```

Summary

The idea is simple:

If you are running out of disk space on a LV, take available from the VG.
If there isn’t disk space available in the VG, add a PV.