Infrastructure & Operations › Linux & Servers

LVM

Flexible logical volumes on top of physical disks.

Also known as: LVM, logical volume manager, logical volumes

LVM (Logical Volume Management) inserts a flexible layer between physical disks and the filesystems on top of them. Instead of formatting a partition directly, you build volumes you can grow, move and snapshot while the system runs.

Three layers:

• Physical volumes (PVs) — disks or partitions marked for LVM.
• Volume groups (VGs) — a pool of space made from one or more PVs.
• Logical volumes (LVs) — the usable slices; a filesystem goes on top.

pvs / vgs / lvs                     # show the pieces
lvextend -r -L +10G /dev/vg0/data   # grow the LV and resize the filesystem

The payoff is that space is pooled. If /data fills up and another disk has room, you add a PV to the VG and extend the LV — no repartitioning, no downtime. You can also snapshot an LV before a risky change.

The classic mistakes:

• Assuming you can shrink anything. Growing is routine; shrinking is not. ext4 can be shrunk but must be unmounted first (and checked), while xfs cannot be shrunk at all. Plan for growth, not shrinkage.
• Forgetting to resize the filesystem. Extending the LV without -r (or a separate resize) leaves free space the filesystem can’t see.
• Thin pools filling silently. On thin-provisioned setups, overcommitted space is only real when written. A pool can fill and take down every volume on it. Monitor it.
• Treating a snapshot as a backup. An LV snapshot shares the original’s disk and grows as data changes; it protects against a bad change, not a failed disk. Keep backups.

When not to use it: a simple single-disk server may be fine with plain partitions. LVM earns its place when you need to grow volumes online, pool disks, or snapshot — common on servers and for disaster recovery workflows.