TopolearnGrowing a full volume without downtime is a routine but nerve-wracking task unless you know LVM.
A disk is divided into partitions described by a partition table. GPT is the modern standard (large disks, many partitions, required for UEFI boot); the older MBR is limited to 2 TiB. Create partitions with fdisk, gdisk or scriptable parted, then let the kernel re-read the table (partprobe).
LVM (Logical Volume Manager) adds a flexible layer between disks and filesystems:
- physical volumes (PV): disks or partitions initialised with
pvcreate, - a volume group (VG): a pool built from one or more PVs with
vgcreate, - logical volumes (LV): virtual block devices carved from the pool with
lvcreate, used like partitions at/dev/vgname/lvname.
The payoff: when a volume fills up, add a disk to the VG (vgextend) and grow the LV while mounted with lvextend -r, where -r also resizes the filesystem. ext4 and XFS can grow online; only ext4 can shrink, and only unmounted. pvs, vgs and lvs summarise the layout.
Snapshots (lvcreate -s) freeze a point-in-time view, handy before an upgrade or for consistent backups; they consume space as the origin changes, so remove them afterwards.
In the cloud you often grow the disk itself: resize it in the provider, then growpart the partition and resize the PV or filesystem. Always take a backup before touching partition tables.
Example
sudo fdisk -l /dev/sdb # current partition table
sudo parted /dev/sdb --script mklabel gpt mkpart data 1MiB 100%
# LVM: physical volumes -> volume group -> logical volumes
sudo pvcreate /dev/sdb1 /dev/sdc1
sudo vgcreate vgdata /dev/sdb1 /dev/sdc1
sudo lvcreate -n lvapp -L 50G vgdata
sudo mkfs.xfs /dev/vgdata/lvapp
sudo pvs; sudo vgs; sudo lvs # summaries
# Out of space? Add a disk and grow online:
sudo pvcreate /dev/sdd1 && sudo vgextend vgdata /dev/sdd1
sudo lvextend -r -L +20G /dev/vgdata/lvapp # -r grows the filesystem too
sudo lvcreate -s -n before-upgrade -L 5G /dev/vgdata/lvapp # snapshot
# Cloud disk resized in the console instead:
sudo growpart /dev/nvme0n1 1 && sudo resize2fs /dev/nvme0n1p1 # (xfs_growfs for XFS)Remember
- GPT partition tables; MBR only for legacy
- LVM: PV -> VG -> LV, grow online with lvextend -r
- Snapshots before risky changes; remove them afterwards
Watch out for
- Extending the logical volume but forgetting to grow the filesystem, so df shows no change.