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💾 Chapter 11: Disk & Storage Management

Intermediate Chapter 11

📑 Table of Contents

Storage Concepts

┌──────────────────────────────────────┐
│          Physical Disk               │
│  (e.g., /dev/sda — 500 GB)          │
├──────────┬──────────┬────────────────┤
│ /dev/sda1│ /dev/sda2│ /dev/sda3      │
│  (boot)  │  (root)  │ (home)         │
│  512 MB  │  50 GB   │ 449.5 GB       │
│  ext4    │  ext4    │ ext4           │
│  /boot   │  /       │ /home          │
└──────────┴──────────┴────────────────┘

Naming Convention

Device Path Description
First SATA/SCSI disk /dev/sda Entire disk
First partition /dev/sda1 First partition on sda
Second partition /dev/sda2 Second partition on sda
NVMe SSD /dev/nvme0n1 First NVMe drive
NVMe partition /dev/nvme0n1p1 First partition on NVMe
Virtual disk /dev/vda Virtio disk (VMs)

Listing Disks & Partitions

# List block devices (most readable)
lsblk
# NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
# sda      8:0    0   500G  0 disk
# ├─sda1   8:1    0   512M  0 part /boot
# ├─sda2   8:2    0    50G  0 part /
# └─sda3   8:3    0 449.5G  0 part /home

lsblk -f                        # Show filesystem types
lsblk -o NAME,SIZE,TYPE,FSTYPE,MOUNTPOINT  # Custom columns

# fdisk list (detailed)
sudo fdisk -l                    # All disks and partitions
sudo fdisk -l /dev/sda           # Specific disk

# Partition information
sudo parted -l                   # List all disk layouts
cat /proc/partitions             # Kernel's view of partitions

# Get UUIDs
sudo blkid                       # Block device IDs
ls -l /dev/disk/by-uuid/         # UUID symlinks

Partitioning Disks

⚠️ Warning: Partitioning can destroy data. Always back up first and practice on VMs!

Using fdisk (MBR)

sudo fdisk /dev/sdb              # Open fdisk for disk sdb

# fdisk commands (interactive):
# m → Help menu
# p → Print partition table
# n → New partition
# d → Delete partition
# t → Change partition type
# w → Write changes and exit
# q → Quit without saving

Using parted (GPT — recommended for modern systems)

sudo parted /dev/sdb

# Interactive commands:
# print          → Show partition table
# mklabel gpt    → Create GPT partition table
# mkpart primary ext4 1MiB 100GiB  → Create partition
# rm 1           → Delete partition 1
# quit           → Exit

# Non-interactive examples:
sudo parted /dev/sdb mklabel gpt
sudo parted /dev/sdb mkpart primary ext4 1MiB 50GiB
sudo parted /dev/sdb mkpart primary ext4 50GiB 100%

MBR vs GPT

Feature MBR GPT
Max disk size 2 TB 9.4 ZB
Max partitions 4 primary (or 3 + extended) 128
Boot mode BIOS (Legacy) UEFI
Redundancy No backup Backup header at end of disk
Recommended Old systems Modern systems ✅

Filesystems

Creating Filesystems

# ext4 (most common for Linux)
sudo mkfs.ext4 /dev/sdb1

# XFS (RHEL default, great for large files)
sudo mkfs.xfs /dev/sdb1

# Btrfs (modern, CoW, snapshots)
sudo mkfs.btrfs /dev/sdb1

# FAT32 (USB drives, cross-platform)
sudo mkfs.vfat -F 32 /dev/sdb1

# exFAT (large files, cross-platform)
sudo mkfs.exfat /dev/sdb1

Filesystem Comparison

Filesystem Max File Max Volume Journaling Use Case
ext4 16 TB 1 EB ✅ General purpose
XFS 8 EB 8 EB ✅ Large files, servers
Btrfs 16 EB 16 EB ✅ CoW Snapshots, NAS
ZFS 16 EB 256 ZB ✅ CoW Enterprise storage
FAT32 4 GB 2 TB ❌ USB, compatibility
exFAT 128 PB 128 PB ❌ Large USB/SD

Filesystem Check & Repair

# Check filesystem (MUST unmount first!)
sudo umount /dev/sdb1
sudo fsck /dev/sdb1              # Automatic detection
sudo fsck.ext4 /dev/sdb1         # Specific to ext4
sudo e2fsck -f /dev/sdb1         # Force check

# XFS check (can be done mounted, read-only)
sudo xfs_repair /dev/sdb1

Mounting & Unmounting

Mounting

# Create mount point
sudo mkdir -p /mnt/mydisk

# Mount a partition
sudo mount /dev/sdb1 /mnt/mydisk

# Mount with specific filesystem type
sudo mount -t ext4 /dev/sdb1 /mnt/mydisk

# Mount read-only
sudo mount -o ro /dev/sdb1 /mnt/mydisk

# Mount with options
sudo mount -o rw,noexec,nosuid /dev/sdb1 /mnt/mydisk

# Mount by UUID (preferred — doesn't change if disk order changes)
sudo mount UUID="xxxx-xxxx-xxxx" /mnt/mydisk

# Mount an ISO file
sudo mount -o loop image.iso /mnt/iso

# Mount a USB drive (usually auto-detected)
sudo mount /dev/sdb1 /mnt/usb

# Mount NFS share
sudo mount -t nfs server:/share /mnt/nfs

# Remount with different options (without unmounting)
sudo mount -o remount,rw /mnt/mydisk

Unmounting

sudo umount /mnt/mydisk          # By mount point
sudo umount /dev/sdb1            # By device

# Force unmount (if busy)
sudo umount -f /mnt/mydisk

# Lazy unmount (detach now, cleanup when not busy)
sudo umount -l /mnt/mydisk

# Find what's using the mount
lsof +D /mnt/mydisk
fuser -vm /mnt/mydisk

View Current Mounts

mount                            # All current mounts
mount | grep sdb                 # Filter for specific disk
findmnt                          # Tree view of mounts
findmnt -t ext4                  # Only ext4 mounts
df -hT                           # Mounts with filesystem type

The /etc/fstab File

/etc/fstab defines filesystems to mount automatically at boot.

cat /etc/fstab

Format

# <device>                              <mount>   <type>  <options>       <dump> <pass>
UUID=xxxx-xxxx-xxxx-xxxx               /          ext4    errors=remount-ro  0      1
UUID=yyyy-yyyy-yyyy-yyyy               /home      ext4    defaults           0      2
UUID=zzzz-zzzz-zzzz-zzzz              /boot      ext4    defaults           0      2
UUID=aaaa-aaaa-aaaa-aaaa              none       swap    sw                 0      0
tmpfs                                  /tmp       tmpfs   defaults,noatime   0      0
Field Description Common Values
device UUID, LABEL, or device path UUID=..., /dev/sda1
mount Mount point /home, /mnt/data
type Filesystem type ext4, xfs, swap, nfs
options Mount options defaults, noatime, ro
dump Backup flag 0 (no), 1 (yes)
pass fsck order 0 (skip), 1 (root), 2 (other)

Common Mount Options

Option Description
defaults rw, suid, dev, exec, auto, nouser, async
noatime Don't update access times (performance boost)
noexec Prevent execution of binaries
nosuid Ignore SUID/SGID bits
ro Read-only
rw Read-write
auto Mount at boot
noauto Don't mount at boot
user Allow normal users to mount
nofail Don't halt boot if device missing 
# Test fstab without rebooting
sudo mount -a                    # Mount everything in fstab

# Always test fstab before rebooting!
sudo findmnt --verify            # Verify fstab syntax

🚨 A broken /etc/fstab can prevent your system from booting. Always test with mount -a before rebooting.

Disk Usage & Space

# Disk free space
df -h                            # Human-readable
df -hT                           # Include filesystem type
df -h /home                      # Specific mount point
df -i                            # Inode usage

# Directory sizes
du -sh /var/log                  # Total size of directory
du -sh /var/*                    # Size of each item in /var
du -sh * | sort -rh | head -10   # Top 10 largest items
du -ah . | sort -rh | head -20   # Top 20 largest files (recursive)

# ncdu — interactive disk analyzer
sudo apt install ncdu
ncdu /                           # Interactive usage viewer

Swap Space

Swap is disk space used when RAM is full — acts as "overflow" memory.

Check Current Swap

swapon --show                    # Active swap spaces
free -h                          # Memory + swap overview
cat /proc/swaps                  # Kernel's swap info

Create Swap File

# Create a 4 GB swap file
sudo fallocate -l 4G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile

# Make permanent — add to fstab
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

# Verify
swapon --show
free -h

Adjust Swappiness

# Check current swappiness (0-100, lower = use swap less)
cat /proc/sys/vm/swappiness      # Default: 60

# Temporary change
sudo sysctl vm.swappiness=10

# Permanent change
echo "vm.swappiness=10" | sudo tee -a /etc/sysctl.conf

🏋️ Practice Exercises

  1. List all block devices with lsblk -f
  2. Check disk usage of /var and find the largest subdirectory
  3. UUID: Find the UUID of your root partition with sudo blkid
  4. fstab: Read your /etc/fstab and identify each entry
  5. Swap: Check your current swap space and swappiness value
  6. Mount: Mount a USB drive or ISO file to /mnt/test
  7. ncdu: Install ncdu and find the largest directory on your system
  8. (VM only): Create a new partition, format it as ext4, and mount it

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