Rocky 9: grow an LVM volume and XFS (tested)

Test scope

Executed in a Rocky Linux 9.8 privileged container (Rocky 9.8 userspace, host kernel 5.14.0-687.54.1.el9_8) with a 2 GB loop file: pvcreate → vgcreate → lvcreate -Z n → dmsetup mknodes → mkfs.xfs → mount → lvextend → xfs_growfs → cleanup. Log: plans/content-expansion/evidence/logs/rocky-storage-lvm.log.

This is not a full virtual machine: the container shares the host kernel and has no udev by default, which is why the dmsetup mknodes step appears below. A real Rocky host does not need it.

Why the extra dmsetup step

lvcreate -y -Z n -L 1G -n lvdata vglab
dmsetup mknodes
ls /dev/mapper/

/dev/mapper/vglab-lvdata

Without udev, lvcreate succeeds but no node appears under /dev/mapper/, so mkfs.xfs /dev/vglab/lvdata fails with “device not found”. dmsetup mknodes creates the node manually. On a real host udev does this automatically.

Create PV/VG/LV and format

sudo dnf install -y lvm2 xfsprogs
truncate -s 2G /var/tmp/lvm-lab.img
LOOP=$(sudo losetup -f --show /var/tmp/lvm-lab.img)
sudo pvcreate -y "$LOOP"
sudo vgcreate vglab "$LOOP"
sudo lvcreate -y -Z n -L 1G -n lvdata vglab
sudo dmsetup mknodes
sudo mkfs.xfs -q /dev/mapper/vglab-lvdata

-Z n skips the wipe and avoids the container error “device not cleared”; a real host can omit it.

Growing takes two steps

sudo mount /dev/mapper/vglab-lvdata /mnt/lvmlab
df -h /mnt/lvmlab | tail -1
sudo lvextend -L +512M /dev/mapper/vglab-lvdata
df -h /mnt/lvmlab | tail -1

/dev/mapper/vglab-lvdata  960M   39M  922M   5% /mnt/lvmlab
Logical volume vglab/lvdata successfully resized.
/dev/mapper/vglab-lvdata  960M   39M  922M   5% /mnt/lvmlab

Growing only the LV leaves df unchanged — the step most often missed.

Grow the filesystem

sudo xfs_growfs /mnt/lvmlab | tail -1
df -h /mnt/lvmlab | tail -1

data blocks changed from 262144 to 393216
/dev/mapper/vglab-lvdata  1.5G   43M  1.4G   3% /mnt/lvmlab

xfs_growfs takes the mount point; ext4 needs resize2fs <device> instead.

Clean up

sudo umount /mnt/lvmlab
sudo dmsetup remove vglab-lvdata
sudo vgremove -y vglab
sudo pvremove -y "$LOOP"
sudo losetup -d "$LOOP"
rm -f /var/tmp/lvm-lab.img

In a container remove the dm device before vgremove, otherwise the loop device stays busy and losetup -d fails.

Common traps

• lvextend without xfs_growfs: df keeps the old value;
• Forgetting dmsetup mknodes in a container: both mkfs and mount report a missing device;
• Trying to shrink XFS: unsupported — back up and recreate.

Practice: run a safe grow

On any Rocky 9 (or AlmaLinux 9) host:

sudo dnf install -y lvm2 xfsprogs
truncate -s 2G /var/tmp/lab.img
LOOP=$(sudo losetup -f --show /var/tmp/lab.img)
sudo pvcreate -y "$LOOP" && sudo vgcreate vglab "$LOOP"
sudo lvcreate -y -L 1G -n lvdata vglab
sudo mkfs.xfs -q /dev/vglab/lvdata
sudo mkdir -p /mnt/lvmlab && sudo mount /dev/vglab/lvdata /mnt/lvmlab
sudo lvextend -L +512M /dev/vglab/lvdata && sudo xfs_growfs /mnt/lvmlab
df -h /mnt/lvmlab

Checks:

1. lvs vglab → 1.50g
2. df -h /mnt/lvmlab → about 1.5G
3. xfs_info /mnt/lvmlab | grep data → blocks 393216

FAQ

常见问题

df did not change after lvextend — did the grow fail?

No. lvextend grows the logical volume (the block device); the filesystem still uses its old size. For XFS run xfs_growfs <mountpoint>, for ext4 resize2fs <device>, and df updates.

mkfs says the device does not exist inside a container?

Containers usually lack udev, so no node appears under /dev/mapper after lvcreate. Run dmsetup mknodes and use /dev/mapper/<vg>-<lv>; a real host does not need this.

Does growing affect running services?

Both lvextend and xfs_growfs work online without unmounting. Still confirm free extents in the VG, verify the mount point, and avoid rebooting or unmounting during the operation.

Next steps

• Post-install checks: 7 checks after install
• Log rotation: logrotate in practice
• Package management: dnf transaction rollback