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Purpose

LVM automatically saves Volume Group metadata. These archives can undo an incorrect LVM change, such as accidentally shrinking a logical volume.

The common mistake is:

lvresize -L 20M /dev/vg_lab/lv_data

This sets the LV to exactly 20 MiB. To add 20 MiB, use:

lvresize -L +20M /dev/vg_lab/lv_data

LVM Structure

Physical Device → PV → VG → LV → Filesystem → Mount Point

Example:

/dev/sdb → vg_lab → lv_data → XFS → /mnt/lvm-demo

Common LV paths:

/dev/vg_lab/lv_data
/dev/mapper/vg_lab-lv_data

Metadata Backups and Archives

Historical metadata is stored in:

/etc/lvm/archive/

The archive usually represents the VG state before a change.

Current metadata is stored in:

/etc/lvm/backup/

Use the archive created immediately before the bad command.

List available versions:

vgcfgrestore -l vg_lab

Check the Description field to identify the correct archive.

Diagnose the Problem

Check the mount and storage layout:

grep /mnt/lvm-demo /etc/fstab
findmnt /mnt/lvm-demo
lsblk -f
pvs
vgs
lvs

If mounting fails after an accidental LV reduction, inspect the metadata history before making further changes.

Restore Previous Metadata

Unmount the filesystem:

umount /mnt/lvm-demo

Restore the selected archive:

vgcfgrestore -f /etc/lvm/archive/vg_lab_00002-123456789.vg vg_lab

vgcfgrestore restores VG and LV metadata, not deleted files or filesystem contents.

Reactivate the LV:

lvchange -an /dev/vg_lab/lv_data
lvchange -ay /dev/vg_lab/lv_data

Then verify and mount:

lvs
lsblk
mount /mnt/lvm-demo
findmnt /mnt/lvm-demo
df -h /mnt/lvm-demo

Correctly Extend an LV and Filesystem

To add space to an XFS filesystem:

lvextend -r -L +20M /dev/vg_lab/lv_data

The -r option grows the filesystem with the LV.

Without -r:

lvextend -L +20M /dev/vg_lab/lv_data
xfs_growfs /mnt/lvm-demo

Critical Syntax Difference

-L 20M

sets the total size to 20 MiB.

-L +20M

adds 20 MiB to the current size.

Example:

40 MiB + -L 20M  → 20 MiB
40 MiB + -L +20M → 60 MiB

XFS Warning

XFS can grow but normally cannot shrink.

Safe:

lvextend -r -L +1G /dev/vg_lab/lv_data

Dangerous:

lvreduce ...

Reducing an LV beneath an existing XFS filesystem can make it unusable.

Essential Commands

vgcfgrestore -l <VG>
vgcfgrestore -f <archive> <VG>
vgcfgbackup <VG>

pvs
vgs
lvs

lvchange -an /dev/<VG>/<LV>
lvchange -ay /dev/<VG>/<LV>

Recovery Workflow

Check mount and LVM status
        ↓
Review metadata history
        ↓
Select the archive before the bad command
        ↓
Unmount and deactivate the LV
        ↓
Restore metadata with vgcfgrestore
        ↓
Reactivate, mount, and verify

Key points:

/etc/lvm/archive/ = historical metadata
/etc/lvm/backup/  = current metadata

-L 20M  = set size
-L +20M = add space

vgcfgrestore restores LVM metadata, not filesystem files. Recovery works only if the underlying filesystem data has not been overwritten.

References:

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