Logical Volume Manager

LVM layer management — physical volumes, volume groups, logical volumes, snapshots, and online resizing.

Physical Volumes

Show all physical volumes — quick inventory of PV-level storage

sudo pvs

Detailed PV info including PE size, free extents, and UUID

sudo pvdisplay /dev/sda2

Initialize a disk or partition as an LVM physical volume

sudo pvcreate /dev/sdb1

Move all extents off a PV before removing it — online data migration

sudo pvmove /dev/sdb1

Remove PV label after pvmove — allows disk removal or repurposing

sudo pvremove /dev/sdb1

Volume Groups

Show all volume groups — name, PV count, LV count, size, free

sudo vgs

Create a volume group from one or more physical volumes

sudo vgcreate vg_data /dev/sdb1

Extend a VG by adding a new physical volume — online capacity expansion

sudo vgextend vg_data /dev/sdc1

Remove a PV from a VG after pvmove — shrink the VG

sudo vgreduce vg_data /dev/sdb1

Logical Volumes

Show all logical volumes — name, VG, size, attributes

sudo lvs

Detailed LV info including segments, stripes, and allocation policy

sudo lvdisplay /dev/vg_data/lv_home

Create a 20G logical volume in a volume group

sudo lvcreate -L 20G -n lv_home vg_data

Create an LV using 100% of remaining free space — use all of it

sudo lvcreate -l 100%FREE -n lv_data vg_data

Extending and Resizing

Extend an LV by 10G and resize the filesystem in one step — ext4/xfs

sudo lvextend -L +10G --resizefs /dev/vg_data/lv_home

Extend to fill all free space in the VG and grow filesystem

sudo lvextend -l +100%FREE --resizefs /dev/vg_data/lv_home

Resize ext4 filesystem manually after lvextend (if --resizefs was omitted)

sudo resize2fs /dev/vg_data/lv_home

Grow XFS filesystem manually — xfs only grows, never shrinks

sudo xfs_growfs /mnt/data

Reducing (Dangerous)

Reduce an ext4 LV — UNMOUNT FIRST, e2fsck required, data loss risk

sudo umount /mnt/home
sudo e2fsck -f /dev/vg_data/lv_home
sudo resize2fs /dev/vg_data/lv_home 15G
sudo lvreduce -L 15G /dev/vg_data/lv_home
sudo mount /dev/vg_data/lv_home /mnt/home

XFS cannot be reduced. Btrfs can shrink but requires btrfs filesystem resize. Always back up before reducing.

Snapshots

Create a snapshot of an LV — COW, size is for changed blocks only

sudo lvcreate -s -L 5G -n lv_home_snap /dev/vg_data/lv_home

Mount a snapshot read-only for backup or inspection

sudo mount -o ro /dev/vg_data/lv_home_snap /mnt/snap

Remove a snapshot after backup — frees COW space

sudo lvremove /dev/vg_data/lv_home_snap

Check snapshot usage — if it fills 100% the snapshot is invalid

sudo lvs -o lv_name,data_percent,origin

Thin Provisioning

Create a thin pool — overcommit storage, allocate on write

sudo lvcreate -L 50G --thinpool thin_pool vg_data

Create a thin LV from the pool — virtual size can exceed pool

sudo lvcreate -V 100G --thin -n thin_vol vg_data/thin_pool

Monitor thin pool usage — critical to avoid overcommit exhaustion

sudo lvs -o lv_name,lv_size,data_percent,metadata_percent vg_data/thin_pool

RHCSA Patterns

Full workflow — disk to mounted filesystem (exam pattern)

sudo pvcreate /dev/sdb1
sudo vgcreate vg_exam /dev/sdb1
sudo lvcreate -L 500M -n lv_exam vg_exam
sudo mkfs.ext4 /dev/vg_exam/lv_exam
sudo mkdir -p /mnt/exam
sudo mount /dev/vg_exam/lv_exam /mnt/exam
echo '/dev/vg_exam/lv_exam /mnt/exam ext4 defaults 0 2' | sudo tee -a /etc/fstab

Verify LVM state end-to-end — confirm PV, VG, LV, and mount

sudo pvs && sudo vgs && sudo lvs && df -h /mnt/exam