Storage & disk management

Disks, partitions, filesystems, and mount points are four different layers that often get flattened into "just storage" — worth pulling apart once so disk errors make sense later.

lsblk                    # see disks and their partitions, as a tree
df -h                    # disk usage per mounted filesystem, human-readable
du -sh /var/log         # how much space one directory is actually using

# the basic path: partition -> filesystem -> mount
sudo fdisk /dev/sdb              # create a partition, interactively
sudo mkfs.ext4 /dev/sdb1         # format it with a filesystem
sudo mount /dev/sdb1 /mnt/data   # attach it into the filesystem tree
sudo umount /mnt/data

A plain partition is fixed in size once created — resizing it later means downtime and risk. LVM (Logical Volume Manager) adds a flexible layer on top: combine multiple physical disks into one pool, then carve out logical volumes that can be resized or extended live.

sudo pvcreate /dev/sdb /dev/sdc          # mark disks as physical volumes
sudo vgcreate data-vg /dev/sdb /dev/sdc  # pool them into a volume group
sudo lvcreate -L 100G -n lv-data data-vg   # carve out a logical volume
sudo mkfs.ext4 /dev/data-vg/lv-data
sudo lvextend -L +20G /dev/data-vg/lv-data   # grow it later, live, no downtime

Add an entry to /etc/fstab so a mount survives a reboot instead of vanishing until someone remounts it by hand.