Storage / Stage 6 of 11

Logical volumes and growing a filesystem

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Step 6 of 7 · lab · 25 min

Grow the data volume

There is almost no space left in /data, and the data must not be deleted. Give the volume more room without repartitioning or losing data.

Situation

A service writes orders to /data, and the space there has almost run out, as df -h /data shows. The orders must not be deleted, and a new disk will not arrive soon.

Task

Make sure that:

the volume holding /data is larger than 200 MiB;
the filesystem at /data has grown with it;
the data in /data is intact: the same files with the same contents.

Constraints

Do not repartition disks or recreate the filesystem.

The tools you need are already installed. There's no internet on this machine.

Lab · on your own

No commands are given in this lab: type them in the terminal yourself. Goals are checked on the machine after every command.

Goals

0 of 3

The volume under /data is larger than 200 MiB — not done yet
The filesystem at /data is larger than 200 MiB — not done yet
The data on /data is intact — not done yet

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Starts the machine node1 · Ubuntu 24.04

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Lab goals

0 of 3

The volume under /data is larger than 200 MiB — not done yet
The filesystem at /data is larger than 200 MiB — not done yet
The data on /data is intact — not done yet

node1 Ubuntu 24.04

Lab goals

0 of 3

The volume under /data is larger than 200 MiB — not done yet
The filesystem at /data is larger than 200 MiB — not done yet
The data on /data is intact — not done yet

Storage and file systems · picked for this lab

LVM logical volumes

Cheat sheet

$_ — insert into the terminal

lsblk block device tree
pvs physical volumes
vgs volume groups
lvs logical volumes
sudo lvextend -r -l +100%FREE /dev/vg/lv extend the LV+fs onto all free space
sudo vgextend vg /dev/sdc add a disk to the group
sudo lvcreate -L 2G -s -n snap /dev/vg/lv a snapshot
sudo lvconvert --merge /dev/vg/snap roll back to the snapshot

Commands by layer

Layer	Create	Show	Extend
PV	`pvcreate /dev/sdb`	`pvs`	—
VG	`vgcreate data /dev/sdb`	`vgs`	`vgextend data /dev/sdc`
LV	`lvcreate -L 10G -n vol1 data`	`lvs`	`lvextend -r -L +5G ...`

bash

lsblk                             # the block device tree (what's inside what)
pvs
vgs
lvs                                # a quick status of each layer
vgs -o +vg_free                   # how much free space is left in the group

Creating and extending

bash

# from scratch:
sudo pvcreate /dev/sdb
sudo vgcreate data /dev/sdb
sudo lvcreate -L 10G -n vol1 data           # fixed size
sudo lvcreate -l 100%FREE -n vol1 data      # take all the VG's free space
sudo mkfs.ext4 /dev/data/vol1
sudo mount /dev/data/vol1 /mnt/vol1

# EXTENDING (the most common task):
sudo vgextend data /dev/sdc                  # add a disk to the group (if the VG is full)
sudo lvextend -r -L +5G /dev/data/vol1       # +5G to the LV AND grow the fs right away (-r)
sudo lvextend -r -l +100%FREE /dev/data/vol1 # give the volume all remaining free space
# manually, without -r:
sudo lvextend -L +5G /dev/data/vol1
sudo resize2fs /dev/data/vol1                # ext4 (xfs: sudo xfs_growfs /mnt/vol1)

Snapshots and moving data

bash

# a snapshot (for backup/rollback; needs free space in the VG):
sudo lvcreate -L 2G -s -n vol1_snap /dev/data/vol1   # -s: snapshot
sudo mount -o ro /dev/data/vol1_snap /mnt/snap        # mount it to copy from
sudo lvconvert --merge /dev/data/vol1_snap            # ROLL BACK to the snapshot
sudo lvremove /dev/data/vol1_snap                     # remove the snapshot

# move data off a disk and drop it from the VG:
sudo pvmove /dev/sdb              # evacuate extents from sdb onto the other PVs
sudo vgreduce data /dev/sdb      # remove the disk from the group

Extended the LV, but there's no extra space

The LV isn't the filesystem. After lvextend, grow the filesystem itself: resize2fs (ext4) or xfs_growfs (xfs). Or use lvextend -r directly.

vgs shows little free space (VFree=0)

The group is full — add a PV: pvcreate /dev/sdc + vgextend data /dev/sdc.

A snapshot "overflowed" and became invalid

A snapshot stores changes; if the original volume is written to heavily and the snapshot is too small, it overflows (lvs shows 100%). Size snapshots generously and take the copy quickly.

The volume is missing after a reboot

sudo vgchange -ay (activate it), and check auto-activation and /etc/fstab (mount by /dev/<vg>/<lv> or UUID).

Accidentally ran lvremove on the wrong volume

Data is gone. Before lvremove/lvreduce, always double-check against lvs and make a snapshot/backup.

Danger. lvremove deletes a logical volume and its data with no way to undo it; vgremove/pvremove destroy the group's and physical volume's metadata entirely. Cross-check against lvs/vgs and confirm a backup exists before deleting — verify by UUID or mount point, not just by name.

Running mkfs on top of an existing LV wipes its filesystem and data just as irreversibly as on a regular partition. lvconvert --merge to roll back to a snapshot irreversibly loses every change made after the snapshot was taken.

Logical volumes and growing a filesystem

Situation

Task

Constraints

Signing in is needed to start the machine

Commands by layer

Creating and extending

Snapshots and moving data

Extended the LV, but there's no extra space

vgs shows little free space (VFree=0)

A snapshot "overflowed" and became invalid

The volume is missing after a reboot

Accidentally ran lvremove on the wrong volume