Assign physical volumes to volume groups

5. Configure Local Storage

📘Red Hat Certified System Administrator (RHCSA – EX200)

In Linux, when you work with storage, Logical Volume Management (LVM) lets you manage disk storage more flexibly. There are three key layers:

Physical Volume (PV) – A real storage device or partition.
Volume Group (VG) – A pool of storage made by combining one or more PVs.
Logical Volume (LV) – The storage you actually use, carved out from VGs.

In this section, we focus on how to assign physical volumes to volume groups.

Step 1: Understand the components

Physical Volume (PV)
- A PV is a disk or partition you prepare for LVM.
- You “initialize” a disk as a PV using the pvcreate command.
- Example: sudo pvcreate /dev/sdb
  sudo pvcreate /dev/sdc
Volume Group (VG)
- A VG is a collection of PVs. Think of it as a storage pool.
- You create a VG using the vgcreate command and assign PVs to it.

Step 2: Create a Volume Group (VG) with PVs

When you assign PVs to a VG, you combine the storage space of multiple disks. This makes management easier and more flexible.

Command syntax:

sudo vgcreate <VG_NAME> <PV1> <PV2> ...

Example:
You have two PVs /dev/sdb and /dev/sdc. You want to create a VG called data_vg.

sudo vgcreate data_vg /dev/sdb /dev/sdc

data_vg is the volume group name.
/dev/sdb and /dev/sdc are the PVs being added.
After this, the VG will show total space as the sum of the PVs.

Check the result:

sudo vgdisplay data_vg

This shows:

Total physical volumes in the VG
Total space available
Free space

Step 3: Add more PVs to an existing VG

Sometimes, you need more storage. You can assign additional PVs to an existing VG using vgextend.

Command syntax:

sudo vgextend <VG_NAME> <NEW_PV>

Example:

sudo vgextend data_vg /dev/sdd

/dev/sdd is a new physical volume added to the data_vg volume group.
The total storage in the VG now increases.

Check updated VG:

sudo vgdisplay data_vg

You’ll see the new total space.

Step 4: Removing PVs from a VG (Optional but Exam Relevant)

If a PV is no longer needed in a VG, you can remove it using vgreduce.

Example:

sudo vgreduce data_vg /dev/sdc

This removes /dev/sdc from data_vg.
Important: The PV must not contain data in logical volumes; otherwise, the system will prevent removal.

Check:

sudo vgdisplay data_vg

Step 5: Key Exam Notes

Commands to remember:
- pvcreate – Initialize a physical volume.
- vgcreate – Create a volume group with PVs.
- vgextend – Add PVs to an existing VG.
- vgreduce – Remove PVs from a VG.
- vgdisplay – Show details of the volume group.
VG concept:
- A VG combines multiple PVs into a single storage pool.
- Storage from a VG can later be divided into Logical Volumes (LVs) for actual use.
Why it’s important for the exam:
- The exam may ask you to create a VG with specific PVs, or add/remove PVs from a VG.
- You should understand how PVs combine into VGs and how to check space.

Step 6: Visual Representation (Simplified)

PV: /dev/sdb  ----\
PV: /dev/sdc  ----->  VG: data_vg  ---> Logical Volumes (LVs)
PV: /dev/sdd  ----/

PVs are the raw storage.
VG pools them.
LVs are slices you actually use.

Step 7: Quick Example Scenario

You have 3 new disks: /dev/sdb, /dev/sdc, /dev/sdd.
Exam task: Create a VG called project_vg using /dev/sdb and /dev/sdc. Then add /dev/sdd to the VG.

Commands:

sudo pvcreate /dev/sdb /dev/sdc /dev/sdd
sudo vgcreate project_vg /dev/sdb /dev/sdc
sudo vgextend project_vg /dev/sdd
sudo vgdisplay project_vg

✅ That’s everything you need for assigning PVs to VGs for the exam. The key is to know the commands and their purpose, and understand that VGs are pools of PVs.