Master LVM on Linux: Create, Extend, Reduce, and Snapshot Volumes

LVM (Logical Volume Manager) is a Linux storage management mechanism that aggregates physical disks into a pool, allowing dynamic resizing of volumes.

Physical Volume (PV): a physical partition created from a disk or partition.

Volume Group (VG): a collection of PVs, treated as a single storage unit.

Logical Volume (LV): a partition within a VG that can be formatted and used for data.

Physical Extent (PE): the smallest allocation unit in a VG, default 4 MiB, configurable.

Create/Remove Physical Volumes (PV)

Use existing disks (e.g., /dev/sdb /dev/sdc) and add them to a PV.

# ll /dev/sd[b-z]
brw-rw---- 1 root disk 8,16 Sep 21 22:04 /dev/sdb
brw-rw---- 1 root disk 8,32 Sep 21 22:04 /dev/sdc
# pvcreate /dev/sdb /dev/sdc   # create PVs
# pvremove /dev/sdc            # remove a PV
# pvs
PV   VG   Fmt Attr PSize PFree
/dev/sda2 centos lvm2 a-- <9.00g 0
/dev/sdb  lvm2   --- 10.00g 10.00g

Create a Volume Group (VG)

Create a VG from existing PVs.

# vgcreate -s [PE size] [VG name] [PV paths...]
# vgcreate -s 4M my_vg /dev/sdb /dev/sdc
# vgs
VG   #PV #LV #SN Attr VSize VFree
centos 1 2 0 wz--n- <9.00g 0
my_vg  2 0 0 wz--n- 19.99g 19.99g

Add a New PV to an Existing VG

Extend the VG by adding another PV.

# vgextend my_vg /dev/sdd
# pvs
PV   VG   Fmt Attr PSize PFree
/dev/sda2 centos lvm2 a-- <9.00g 0
/dev/sdb  my_vg  lvm2 a-- <10.00g <10.00g
/dev/sdc  my_vg  lvm2 a-- <10.00g <10.00g
/dev/sdd  my_vg  lvm2 a-- <10.00g <10.00g

Remove a Single PV from a VG

Remove a specific PV from the VG.

# vgreduce my_vg /dev/sdd
# pvs
... (output showing /dev/sdd removed)

Remove an Entire VG

Delete the VG completely.

# vgremove my_vg
Volume group "my_vg" successfully removed

Remove an Empty VG

Remove a VG that has no allocated space.

# vgreduce -a my_vg   # removes only empty VGs

Create a Logical Volume (LV)

Create an LV named my_lv of 10 GiB in my_vg.

# lvcreate -L 10G -n my_lv my_vg
# lvs
LV     VG   Attr   LSize
my_lv  my_vg -wi-a----- 10.00g

Format and Mount the LV

# mkdir /LVM
# mkfs.ext4 /dev/my_vg/my_lv
# mount /dev/my_vg/my_lv /LVM/

Extend LV Capacity

Increase LV size by 5 GiB and resize the filesystem.

# lvextend -L +5G /dev/my_vg/my_lv
# resize2fs -f /dev/my_vg/my_lv

Reduce LV Capacity

Shrink LV from 15 GiB to 10 GiB.

# umount /dev/my_vg/my_lv
# e2fsck -f /dev/my_vg/my_lv
# resize2fs -f /dev/my_vg/my_lv 10G
# lvreduce -L 10G /dev/my_vg/my_lv
# mount /dev/my_vg/my_lv /LVM/

Create an LVM Snapshot

# lvcreate -s -n mylv_back -L 200M /dev/my_vg/my_lv
# lvs   # shows snapshot mylv_back

Restore from a Snapshot

# mkdir /back
# mount /dev/my_vg/mylv_back /back/
# cp -a /back/* ./