Memory hook: Disk to PV to VG to LV to filesystem to mount.
Must remember
Inspect before modifying: lsblk -f, blkid, findmnt, pvs, vgs and lvs reveal the device graph. A partition table such as GPT divides a disk; creating or formatting the wrong device destroys data. Practice only on disposable disks.
LVM layers physical volumes into a volume group, then allocates logical volumes. pvcreate, vgcreate/vgextend and lvcreate operate at those layers. Extending the LV alone does not necessarily grow the filesystem. lvextend -r can resize the supported filesystem as well; understand the underlying operation and available free extents.
XFS can grow while mounted and cannot shrink. ext4 supports growth and can shrink while unmounted with the correct sequence. Never shrink an LV below its filesystem. VFAT suits compatibility but lacks normal Unix ownership/permission semantics; mount options supply effective access behavior.
An ephemeral mount command does not survive reboot. /etc/fstab records source, mountpoint, filesystem type, options, dump and fsck fields. UUIDs or filesystem labels avoid unstable device-name assumptions. Test a change with findmnt --verify and an appropriate mount check before reboot; a bad required mount can interrupt boot.
Swap can use a suitable partition or LV: initialise it with mkswap, activate with swapon, verify with swapon --show, and configure persistence. Do not reinitialise a device containing useful data.
For NFS, match server export, network access and client mount options. autofs uses maps to mount paths on demand and expire idle mounts; verify by accessing the trigger path, not only looking at an idle mount table. Ownership IDs and permissions still matter on shared storage.
Choose under exam pressure
| Requirement | Choice and reason |
|---|---|
| Add capacity without deleting data | Extend the correct LVM layers and filesystem after inspection. |
| Mount after reboot | Use a tested fstab entry with a stable source identifier. |
| Mount NFS only when used | Configure autofs maps and test path access. |
Traps
- XFS does not support shrinking.
- A mounted directory can hide existing files beneath the mountpoint without deleting them.
Active recall
1. What comes between a physical volume and a logical volume?
A volume group pools physical-volume capacity.
2. Does a larger LV guarantee more filesystem space?
No. The filesystem must be grown too.
3. Why use a UUID in fstab?
It identifies the filesystem without relying on changing device enumeration names.
4. Why is an autofs mount absent while idle?
It is activated on demand and may expire when unused.
5. What is the final storage verification?
Check the intended path, capacity, permissions and persistence after a safe reboot test.