Design Hard Disk Layout LVM

Welcome to our in-depth guide on configuring and managing LVM (Logical Volume Manager) storage in Linux. LVM provides dynamic volume resizing, flexible disk pooling, and snapshot capabilities, making it a powerful tool for system administrators.

What You’ll Learn

Installing LVM utilities
Key LVM components: PV, VG, LV, PE
Creating Physical Volumes (PV)
Building and extending Volume Groups (VG)
Allocating and resizing Logical Volumes (LV)
Formatting and resizing filesystems
Common commands and handy tips

Prerequisites

We’ve attached three new 5 GiB virtual disks to our CentOS VM. If you haven’t installed the LVM tools yet, run:

sudo dnf install lvm2

Note

Most LVM operations require root privileges. Prepend sudo or switch to the root user before proceeding.

LVM Abbreviations

Resource	Description	Command Prefix
Physical Volume (PV)	A disk or partition managed by LVM	`pv*`
Volume Group (VG)	A pool of one or more PVs	`vg*`
Logical Volume (LV)	A virtual partition carved from a VG	`lv*`
Physical Extent (PE)	The smallest allocation unit in LVM	n/a

1. Creating Physical Volumes (PV)

Physical Volumes are the foundation of LVM. You can use entire disks or partitions.

Scan for available disks and existing PVs:

sudo lvmdiskscan

Sample output:

/dev/sda1  [   1.00 GiB]
/dev/sda2  [ <19.00 GiB] LVM physical volume
/dev/sdb1  [   4.00 GiB]
/dev/sdc   [   5.00 GiB]
/dev/sdd   [   5.00 GiB]
/dev/sde   [   5.00 GiB]
3 disks
1 LVM physical volume

Initialize /dev/sdc and /dev/sdd as new PVs:
```
sudo pvcreate /dev/sdc /dev/sdd
```

Verify all PVs:

sudo pvs

  PV         VG         Fmt  Attr PSize   PFree
  /dev/sda2  cs         lvm2 a--  <19.00g    0
  /dev/sdc   lvm2 ---   5.00g  5.00g
  /dev/sdd   lvm2 ---   5.00g  5.00g

PFree indicates unallocated space ready for LVs.

2. Building a Volume Group (VG)

Volume Groups aggregate one or more PVs into a single storage pool.

Create a VG named my_volume:

sudo vgcreate my_volume /dev/sdc /dev/sdd

Volume group "my_volume" successfully created

To extend the VG later, initialize another PV:
```
sudo pvcreate /dev/sde
```
Add it to my_volume:
```
sudo vgextend my_volume /dev/sde
```

List all VGs:

sudo vgs

  VG          #PV #LV #SN Attr   VSize   VFree
  cs           1   2   0 wz--n  <19.00g    0
  my_volume    3   0   0 wz--n  14.99g 14.99g

Removing a PV from a VG

Detach /dev/sde:
```
sudo vgreduce my_volume /dev/sde
```
Wipe its metadata:
```
sudo pvremove /dev/sde
```

3. Allocating Logical Volumes (LV)

Logical Volumes are like partitions within a VG.

Create a 2 GiB LV called partition1:

sudo lvcreate --size 2G --name partition1 my_volume

Create a 6 GiB LV called partition2:

sudo lvcreate --size 6G --name partition2 my_volume

View all LVs:

sudo lvs

  LV         VG         Attr       LSize
  partition1 my_volume -wi-a----- 2.00g
  partition2 my_volume -wi-a----- 6.00g

Check remaining VG space:

sudo vgs

  VG         #PV #LV #SN Attr   VSize   VFree
  my_volume   2   2   0 wz--n-  9.99g  1.99g

4. Resizing Logical Volumes

LVM data is allocated in Physical Extents (PE). You can grow or shrink LVs by adjusting their extents.

Grow to Fill Free Space

Expand partition1 to consume all free extents:

sudo lvresize --extents +100%FREE /dev/my_volume/partition1

Shrink Back

Reduce partition1 back to 2 GiB:

sudo lvresize --size 2G /dev/my_volume/partition1

Warning

Shrinking a filesystem without shrinking the filesystem itself first can lead to data loss. Always unmount, run a filesystem check, and resize the filesystem before reducing an LV.

5. Formatting the Filesystem

Before storing data, format your LV. For example, to use XFS:

sudo mkfs.xfs /dev/my_volume/partition1

6. Resizing with an Existing Filesystem

To grow both the LV and its filesystem in one command:

sudo lvresize --resizefs --size 3G /dev/my_volume/partition1

Note: Not all filesystems support online shrinking. Check your filesystem’s documentation.