Manage Basic Storage

🎯 Introduction

Storage management is fundamental to Linux administration. You must understand how to partition disks, create file systems, and mount storage to make it accessible. RHEL supports both MBR (legacy) and GPT (modern) partitioning schemes.

Storage Hierarchy

1. Physical Disk: /dev/sda, /dev/vda, /dev/nvme0n1
2. Partitions: /dev/sda1, /dev/vda2, /dev/nvme0n1p1
3. File System: ext4, XFS, Btrfs
4. Mount Point: /, /home, /data

Device Naming Conventions

🔧 Disk Partitioning

Viewing Disk Information

# List all block devices
lsblk

# Output example:
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   19G  0 part 
  ├─rhel-root 253:0 0 17G 0 lvm  /
  └─rhel-swap 253:1 0  2G 0 lvm  [SWAP]
sdb      8:16   0   10G  0 disk 

# Show filesystem information
lsblk -f

# List partition tables
sudo fdisk -l

# Show disk usage
df -h

# Show partition UUID and filesystem
sudo blkid

Partitioning with fdisk (MBR)

Use fdisk for MBR partition tables (disks ≤ 2TB):

# Start fdisk
sudo fdisk /dev/sdb

# Commands within fdisk:
m     # Help
p     # Print partition table
n     # New partition
d     # Delete partition
t     # Change partition type
l     # List partition types
w     # Write changes and exit
q     # Quit without saving

# Example: Create new partition
Command: n
Partition type: p (primary)
Partition number: 1
First sector: (press Enter for default)
Last sector: +2G (create 2GB partition)

# Set partition type to Linux LVM (type 8e)
Command: t
Partition number: 1
Hex code: 8e

# Write changes
Command: w

Partitioning with parted (GPT)

Use parted for GPT partition tables (modern, >2TB disks):

# Start parted in interactive mode
sudo parted /dev/sdb

# Create GPT partition table
(parted) mklabel gpt

# Create partition
(parted) mkpart primary 1MiB 2GiB

# Name the partition
(parted) name 1 data

# Set flags
(parted) set 1 lvm on

# Print partition table
(parted) print

# Quit
(parted) quit

# Non-interactive mode
sudo parted /dev/sdb mklabel gpt
sudo parted /dev/sdb mkpart primary 1MiB 2GiB
sudo parted /dev/sdb name 1 data
sudo parted /dev/sdb set 1 lvm on

Updating Kernel Partition Table

# Inform kernel of partition table changes
sudo partprobe /dev/sdb

# Alternative if partprobe fails
sudo partx -u /dev/sdb

# Verify changes
lsblk /dev/sdb

Deleting Partitions

# With parted
sudo parted /dev/sdb rm 1

# With fdisk
sudo fdisk /dev/sdb
Command: d
Partition number: 1
Command: w

💾 File Systems

RHEL 9 primarily uses XFS (default) and ext4 file systems.

File System Comparison

Creating File Systems

# Create XFS filesystem (RHEL default)
sudo mkfs.xfs /dev/sdb1

# Create ext4 filesystem
sudo mkfs.ext4 /dev/sdb1

# Create with label
sudo mkfs.xfs -L "data" /dev/sdb1
sudo mkfs.ext4 -L "backup" /dev/sdb2

# Force creation (overwrites existing filesystem)
sudo mkfs.xfs -f /dev/sdb1

# Create with specific options
sudo mkfs.ext4 -b 4096 -i 8192 /dev/sdb1
# -b block size
# -i bytes per inode

File System Labels

# Set/change XFS label
sudo xfs_admin -L "newlabel" /dev/sdb1

# Set/change ext4 label
sudo e2label /dev/sdb1 "newlabel"

# View labels
lsblk -f
sudo blkid

Checking and Repairing File Systems

# Check XFS filesystem
sudo xfs_repair /dev/sdb1

# Check ext4 filesystem
sudo fsck.ext4 /dev/sdb1
# or
sudo e2fsck /dev/sdb1

# Force check
sudo e2fsck -f /dev/sdb1

# Automatic repair
sudo e2fsck -p /dev/sdb1

# Interactive repair
sudo e2fsck -y /dev/sdb1

Extending File Systems

# Extend XFS (must be mounted)
sudo xfs_growfs /mount/point

# Extend ext4 (can be mounted or unmounted)
sudo resize2fs /dev/sdb1

# Extend to specific size
sudo resize2fs /dev/sdb1 10G

📂 Mounting File Systems

Manual Mounting

# Create mount point
sudo mkdir /data

# Mount filesystem
sudo mount /dev/sdb1 /data

# Mount with options
sudo mount -o ro /dev/sdb1 /data        # Read-only
sudo mount -o noexec /dev/sdb1 /data    # No execute
sudo mount -o nosuid /dev/sdb1 /data    # Ignore SUID

# Mount by label
sudo mount LABEL=data /data

# Mount by UUID
sudo mount UUID=xxx-xxx-xxx /data

# Verify mount
mount | grep sdb1
df -h /data

Unmounting

# Unmount by device
sudo umount /dev/sdb1

# Unmount by mount point
sudo umount /data

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

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

# Check what's using the mount
sudo lsof /data
sudo fuser -mv /data

Common Mount Options

💱 Swap Space

Swap is used when RAM is full. It can be a partition or a file.

Creating Swap Partition

# Create partition (use partition type 82 for MBR, or 'swap' for GPT)
sudo parted /dev/sdb mkpart primary linux-swap 5GiB 7GiB

# Format as swap
sudo mkswap /dev/sdb2

# Set label
sudo mkswap -L swap1 /dev/sdb2

# Enable swap
sudo swapon /dev/sdb2

# Verify
swapon --show
free -h

Creating Swap File

# Create 2GB swap file
sudo dd if=/dev/zero of=/swapfile bs=1M count=2048
# or faster with fallocate
sudo fallocate -l 2G /swapfile

# Set permissions
sudo chmod 600 /swapfile

# Format as swap
sudo mkswap /swapfile

# Enable swap
sudo swapon /swapfile

# Verify
swapon --show

Managing Swap

# View swap usage
swapon --show
free -h
cat /proc/swaps

# Disable swap
sudo swapoff /dev/sdb2
sudo swapoff /swapfile

# Disable all swap
sudo swapoff -a

# Enable all swap from /etc/fstab
sudo swapon -a

# Check swap priority
swapon --show

Swap Priority

# Enable with priority (higher number = higher priority)
sudo swapon -p 10 /dev/sdb2

# In /etc/fstab:
/dev/sdb2  none  swap  pri=10  0 0

📝 Persistent Mounts (/etc/fstab)

The /etc/fstab file defines filesystems to mount at boot time.

fstab Format

# /etc/fstab
#           

UUID=xxx-xxx   /data         xfs     defaults   0       2
LABEL=backup   /backup       ext4    defaults   0       2
/dev/sdb3      /mnt/extra    xfs     noauto     0       0
/swapfile      none          swap    sw         0       0

Field Descriptions

Getting UUID

# Show all UUIDs
sudo blkid

# Show specific device
sudo blkid /dev/sdb1

# Output:
/dev/sdb1: UUID="xxx-xxx-xxx" TYPE="xfs"

# Use lsblk
lsblk -f

Systemd Mount Units

Alternative to fstab for complex mounts:

# Create mount unit: /etc/systemd/system/data.mount
[Unit]
Description=Data Partition

[Mount]
What=/dev/sdb1
Where=/data
Type=xfs
Options=defaults

[Install]
WantedBy=multi-user.target

# Enable and start
sudo systemctl daemon-reload
sudo systemctl enable --now data.mount