Disk Management Basics - Inspecting Storage with fdisk and lsblk

Disk Management Basics - Inspecting Storage with fdisk and lsblk
Reading time: About 10 min Difficulty: Intermediate

What You'll Learn

  • How to read storage layout with lsblk and fdisk -l
  • The relationship between block devices, partitions, and mount points
  • When to use df vs du for disk space investigation

Quick Summary

  • Check disk layout → lsblk (tree view, no root required)
  • Partition details → sudo fdisk -l (sector boundaries and types)
  • Free space by filesystem → df -h
  • Space used by directory → du -sh *

What is lsblk? Visualizing Block Devices as a Tree

lsblk (list block devices) displays disks, partitions, and mount points in a tree structure. It runs without root privileges, making it the first command to reach for when investigating storage layout.

$ lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
sda      8:0    0   20G  0 disk
├─sda1   8:1    0    1G  0 part /boot
├─sda2   8:2    0    2G  0 part [SWAP]
└─sda3   8:3    0   17G  0 part /
sdb      8:16   0   50G  0 disk
└─sdb1   8:17   0   50G  0 part /data

Column reference:

Column Meaning
NAME Device name (sda = first SATA/SCSI/NVMe disk)
SIZE Device size
TYPE disk (physical disk) / part (partition) / lvm etc.
MOUNTPOINTS Mount target (blank = not mounted)

Show filesystem details with -f

$ lsblk -f
NAME   FSTYPE FSVER LABEL UUID                                 FSAVAIL FSUSE% MOUNTPOINTS
sda
├─sda1 ext4   1.0         a1b2c3d4-...                         800M    20%    /boot
├─sda2 swap   1                                                               [SWAP]
└─sda3 ext4   1.0         e5f6a7b8-...                         14.2G   16%    /

The -f flag adds filesystem type (FSTYPE) and UUID. UUIDs are useful when checking /etc/fstab mount configuration.

What is fdisk -l? Inspecting Partition Tables

fdisk -l (list) shows the full partition table with sector counts and partition types (Linux, Linux swap, EFI System, etc.). Root privileges are required.

$ sudo fdisk -l /dev/sda
Disk /dev/sda: 20 GiB, 21474836480 bytes, 41943040 sectors
Disk model: Virtual disk
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX

Device     Start      End  Sectors  Size Type
/dev/sda1   2048  2099199  2097152    1G Linux filesystem
/dev/sda2  2099200  6293503  4194304    2G Linux swap
/dev/sda3  6293504 41943006 35649503   17G Linux filesystem

Key fields to read:

  • Disklabel type: gpt (GUID Partition Table) or dos (MBR). Modern systems use GPT.
  • Type: Partition role — Linux filesystem, Linux swap, EFI System, etc.
  • Start / End / Sectors: Partition boundaries, useful during disk diagnostics.

To check a specific disk: sudo fdisk -l /dev/sda. To list all disks at once, run sudo fdisk -l with no arguments.

fdisk can also edit partition tables — operations beyond -l (list) risk data loss if used incorrectly. This article covers read-only inspection only.

How Do df and du Fit In?

lsblk and fdisk show the hardware and partition layout. df and du report filesystem usage — what is actually used and free at the OS level.

Command Shows Typical use
lsblk Block device tree structure Understand disk layout
fdisk -l Partition table details Check boundaries and types
df -h Used/free space per filesystem Find which FS is running low
du -sh Size of directories or files Find what is consuming space 
# Space free per filesystem
$ df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda3        17G  2.7G   13G  17% /
/dev/sda1       974M  189M  718M  21% /boot
/dev/sdb1        50G  1.2G   47G   3% /data

# Breakdown by subdirectory
$ du -sh /var/*
48M    /var/cache
1.2G   /var/log
8.0K   /var/mail

If df shows free space but writes fail, check inode exhaustion with df -i. Filesystems have separate limits on blocks and inodes.

Device Naming Conventions

Device names vary by hardware type — a common source of confusion for new users.

Prefix Hardware Examples
/dev/sd* SATA / SCSI / USB / most virtual disks sda, sdb, sdc
/dev/nvme* NVMe SSD nvme0n1, nvme0n1p1
/dev/vd* KVM/QEMU virtual disk vda, vdb
/dev/xvd* Xen virtual disk xvda

NVMe partitions use a p suffix followed by the partition number (nvme0n1p1 = partition 1 on the first NVMe drive).

$ lsblk
NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
nvme0n1     259:0    0  256G  0 disk
├─nvme0n1p1 259:1    0  512M  0 part /boot/efi
├─nvme0n1p2 259:2    0    2G  0 part /boot
└─nvme0n1p3 259:3    0  253G  0 part /

Summary

  • lsblk: First command to run for any disk investigation. No root required.
  • sudo fdisk -l: Detailed partition table including type and sector layout. Root required.
  • df -h: How much space is free on each mounted filesystem.
  • du -sh: Which directories are consuming the most space.

The standard investigation flow: lsblk to map the device layout → df -h to find which filesystem is full → du -sh to pinpoint the large directories within it.

Next Steps