Extending LVM Logical Volume (LV) in Linux – Runbook

[Kalyani]

Purpose
Extend disk space on a Linux system using LVM without downtime.

Applies to
Systems using LVM (Logical Volume Manager)

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 Problem

Filesystem (e.g. /, /var) is running out of space and needs to be extended.

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 Step 1 — Check Current Disk Usage

Code:

df -h

Output:

Code:

/dev/mapper/rootvg-varlv    14G  13G  1.4G  91% /var

Outcome:

• Identify which mount point is full (e.g /var)
  
• This determines which LV needs extension
  

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 Step 2 — Verify LVM Setup (Build Context for Extension)

  1. Map LV to Mount Point

Code:

lsblk

Output :

Code:

NAME              MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
sda                8:0    0  256G  0 disk
├─sda4              8:4    0 63.3G  0 part
  ├─rootvg-varlv  253:3    0  14G  0 lvm  /var

└─sda5              8:5    0  100G  0 part
  ├─rootvg-varlv  253:3    0  14G  0 lvm  /var

 Insight:

• Identifies which LV is mounted where
  
• Confirms LVM usage (TYPE = lvm)
  
  

  2. Identify Target LV

Code:

lvs -o lv_name,vg_name,lv_path

Output:

Code:

LV    VG    Path
varlv  rootvg /dev/rootvg/varlv

 Insight:

• Confirms exact LV name to extend (e.g varlv)
  
• Provides correct device path required for lvextend (e.g  /dev/rootvg/varlv)
  
  

  3. Check Available Space in VG 

Code:

vgs

Output:

Code:

VG    #PV #LV #SN Attr  VSize    VFree
rootvg  2  5  0 wz--n- <163.31g 316.00m

Insight:

• Determines if extension is possible
  

       Interpretation:

• VFree > 0
  → Extend directly
  
• VFree = 0
  → Add disk first
  

  4. Check Underlying Disks

Code:

pvs

Code:

PV        VG    Fmt  Attr PSize    PFree
/dev/sda4  rootvg lvm2 a--  63.31g    0
/dev/sda5  rootvg lvm2 a--  <100.00g 316.00m

 Insight:

• Shows disks backing the VG
  
• Confirms whether storage is already fully utilized
  
  

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 Step 2 Outcome (What we now know)

• Which LV to extend (varlv)
  
• Its mount point (/var) and exact path (/dev/rootvg/varlv)
  
• Whether free space exists in VG
  
• Which disks are backing LVM
  
  

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 Decision Point

Case A: VG has free space
→ Extend LV directly

Case B: No free space
→ Add disk / extend storage first

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Case A — Extend LV (VG has free space)

  Step 3 — Extend Logical Volume

Code:

lvextend -L +316M /dev/rootvg/varlv

• -L → size in GB/MB
  

OR use all free space:

Code:

lvextend -l +100%FREE /dev/rootvg/varlv

• -l → extents / percentage
  

Outcome:

Code:

Size of logical volume rootvg/varlv changed from 14.00 GiB (3584 extents) to <14.31 GiB (3663 extents).
Logical volume rootvg/varlv successfully resized.

• LV size increases
  
• Filesystem unchanged (IMPORTANT)
  

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   Step 4 — Resize Filesystem

Check filesystem:

Code:

lsblk -f

For ext4:

Code:

resize2fs /dev/rootvg/varlv

For xfs:

Code:

xfs_growfs /var

Outcome:

• Filesystem expands to use new space
  
  

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  Step 5 — Verify

Code:

df -h

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Case B — No Free Space in VG

  Step 3 — Add New Disk (Cloud / VM level)

• Add a new disk from your cloud provider / hypervisor (e.g. AWS, Azure, VMware)
  
• Example: New disk appears as /dev/sdb
  
• Verify Disk is Added
  
  Code:

  lsblk
• New disk should be visible (e.g. /dev/sdb)
  

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  Step 4 — Create PV

Code:

pvcreate /dev/sdb

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  Step 5 — Extend VG

Code:

vgextend rootvg /dev/sdb

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  Step 6 — Extend LV

Code:

lvextend -l +100%FREE /dev/rootvg/varlv

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  Step 7 — Resize Filesystem

Code:

xfs_growfs /var

# OR

Code:

resize2fs /dev/rootvg/varlv

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  Step 8 — Verify

Code:

df -h

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 Additional Note — Expanding Existing Disk

If the same disk is increased in size (no new disk added):

Code:

growpart /dev/sda 4

Code:

pvresize /dev/sda4

Outcome:

• growpart → expands the partition
  
• pvresize → makes new space available to LVM
  

 You can now proceed with lvextend

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Common Mistakes

• Extending LV but not resizing filesystem
  
• Using wrong filesystem command (resize2fs vs xfs_growfs)
  
• Not checking vgs before starting
  
• Using wrong device path
  
• Confusing disk (/dev/sdb) with LV (/dev/rootvg/varlv)
  
  

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 Key Concepts and Takeaways

• PV (Physical Volume) → Disk (/dev/sda4)
  
• VG (Volume Group) → Storage pool (rootvg)
  
• LV (Logical Volume) → Usable volume (/var)
  

Flow:
Disk → PV → VG → LV → Filesystem

• Extension = LV resize + filesystem resize
  
• vgs decides your approach (direct vs add disk)
  
• LVM allows online resizing (no downtime)
  

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 Precautions

• Take backup before changes
  
• Double-check device names
  
• Run carefully on production