Master Linux Disk Structure, Partitioning, and File System Management

1. Disk Structure

Physical Structure

Plates: A disk contains multiple platters, each with two surfaces.

Heads: Each surface has a read/write head; the number of heads equals the number of platter surfaces.

Data Structure

Sectors: Each platter is divided into sectors, each storing 512 bytes (the minimum storage unit; partial sectors are rounded up to 512 bytes).

Tracks, Cylinders:

Disk Interface Types

HDD vs. SSD

2. Disk Partitioning

Why Partition?

Optimize I/O performance

Implement space quotas and improve recovery speed

Isolate system and applications

Install multiple operating systems

Use different file system types

Partition Types

Extended partitions cannot be used directly; they must be divided into logical partitions.

Partition Structure

Only four primary partitions are allowed.

Primary and extended partition numbers range from 1 to 4.

Logical partitions start numbering from 5.

3. File Systems

XFS File System

Stores files and directory data

High‑performance journaling file system

Default on CentOS 7 (supports data recovery)

SWAP (Swap File System)

Creates a swap partition for Linux

Other Linux‑Supported File Systems

FAT16, FAT32, NTFS

EXT4, JFS

disk Command

View or manage disk partitions fdisk -l [disk_device] or

fdisk [disk_device]

fdisk -l Output Explanation

Device: partition device name

Boot: indicates bootable partition (marked with "*")

Start: starting cylinder

End: ending cylinder

Blocks: size in 1024‑byte blocks

Id: system ID (e.g., 83 for Linux EXT4, 8e for LVM)

System: partition type

Interactive Mode Commands

m, p, n, d, t, w, q

mkfs Command

Make Filesystem – creates (formats) a file system

Boot partition: used for system boot; "*" marks a bootable partition.

Scan SCSI bus without reboot:

echo "- - -" > /sys/class/scsi_host/host2/scan

Change partition type, delete partition, etc. (illustrated with images).

Typical workflow: partition → format → create mount point → mount.

4. Mounting and Unmounting File Systems

mount Command

Mount a file system or ISO image to a directory

mount [-t type] device mount_point
mount -o loop iso_image_file mount_point

umount Command

Unmount a mounted file system

umount device_path
umount mount_point

These are temporary mounts.

Automatic Mounting via /etc/fstab

The /etc/fstab file lists mount configurations, each line containing six fields separated by spaces or tabs: /dev/sdb1 / xfs defaults 0 0 Field 1: device name or label

Field 2: mount point directory

Field 3: file system type (e.g., xfs, swap)

Field 4: mount options (e.g., defaults, rw, ro, noexec)

Field 5: dump backup flag (1 = backup, 0 = ignore)

Field 6: fsck order (0 = no check, 1 = first, 2 = later)

Adding an entry for /dev/sdb1 enables automatic mounting at boot.

5. Checking Disk Usage

df Command

df [options] [file]

# df -hT
Filesystem     Type  Size  Used  Avail  Use%  Mounted on
/dev/mapper/VolGroup-Lv_root ext4 6.7G 4.1G 2.3G  65%  /
/dev/sda1      ext4   99M  11M   83M  12%  /boot
tmpfs          tmpfs  252M 0    252M   0%  /dev/shm
/dev/sdb1      ext4   19G 173M  18G   1%   /mailbox