Growing an LVM logical volume and its filesystem online without unmounting

Goal

Increase the size of a logical volume (LV) and grow its filesystem to match, while the filesystem stays mounted and in use.

Prerequisites

Root access; an LVM-managed volume group (VG) with free extents, or an underlying block device (disk or partition) that was already enlarged at the storage layer; a recent backup or snapshot, since any LVM metadata operation carries some risk even when only growing.

Steps

1. If the physical device itself was enlarged (a virtual disk resized, or a partition grown), tell LVM to recognize the new size: pvresize /dev/sdX1. Verify with pvs and vgs that free physical extents increased.
2. Extend the LV and resize its filesystem in one step: lvextend -r -L +20G /dev/vgdata/lvhome (or -l +100%FREE to consume all remaining free extents in the VG). The -r/--resizefs flag makes lvextend call the matching filesystem-resize tool automatically after growing the LV.
3. If resizing manually instead of with -r: for XFS, run xfs_growfs /mountpoint — note that it takes the mount point, not the device path, and only grows; XFS filesystems cannot be shrunk at all, by design. For ext4, run resize2fs /dev/vgdata/lvhome; ext4 supports online growth while mounted, using the kernel's on-line resizing support, but shrinking still requires the filesystem to be unmounted first.
4. Verify the result: df -h /mountpoint shows the new size; lvs vgdata/lvhome shows the enlarged LV.

Expected result

The mounted filesystem reports the increased capacity with no downtime and no interruption to processes using it.

Limits and test basis

Based on lvextend(8), pvresize(8), xfs_growfs(8) and resize2fs(8). There is no supported "undo" for growth other than a later shrink (ext4 only, offline) or restoring from the pre-change snapshot/backup; growing an LV does not itself endanger data, but a failed or interrupted resize on ext4 should be followed by e2fsck -f before remounting. Never attempt to shrink an XFS filesystem — the tooling refuses it outright, and the only path is backup, recreate smaller, and restore.