LVM - Logical Volume Manager

LVM

LVM adds a flexible layer between physical disks and filesystems so you can resize storage live.

Physical Volume (PV)  →  Volume Group (VG)  →  Logical Volume (LV)  →  filesystem
   /dev/sdb1                  vg_data              lv_web

Layer	Create	Inspect
PV	`pvcreate /dev/sdb1`	`pvs` / `pvdisplay`
VG	`vgcreate vg_data /dev/sdb1`	`vgs` / `vgdisplay`
LV	`lvcreate -L 10G -n lv_web vg_data`	`lvs` / `lvdisplay`

Grow a volume (the killer feature):

$ lvextend -L +5G /dev/vg_data/lv_web
$ resize2fs /dev/vg_data/lv_web      # ext4 - grow the FS
# xfs_growfs /data                   # xfs equivalent (mounted)

Exam tip: Extending is two steps - grow the LV (lvextend) then grow the filesystem (resize2fs for ext4, xfs_growfs for xfs). xfs can only grow, never shrink.