Disk Partitioning: Building the Foundation

A hard drive is like a new warehouse. Before you can start putting crates (files) inside, you need to build the rooms and hallways. These rooms are called Partitions.

Partitioning is one of the "Danger Zones" for new Linux administrators. A single mistake here can wipe out an entire drive. But it is also where you gain true control over your system's performance and security. In this lesson, we will learn the two main "Blueprints" for disks: MBR and GPT.

1. MBR vs. GPT: Selecting Your Blueprint

I. MBR (Master Boot Record) - The Classic

Age: 40+ years old.
Limit: Maximum of 2 TeraBytes per disk.
Complexity: Only allows 4 "Primary" partitions. To have more, you have to create an "Extended" partition, which is messy.
Fragility: All partition info is stored in one tiny spot at the beginning of the disk. If that spot is damaged, the disk is dead.

II. GPT (GUID Partition Table) - The Modern

Age: 15 years old (standard with UEFI).
Limit: Maximum of 9.4 ZettaBytes (more than all the disks in the world combined).
Simplicity: Allows effectively unlimited primary partitions (128 by default).
Safety: Stores multiple copies of the partition table across the disk. If one is corrupted, Linux repairs it automatically.

Verdict: Always use GPT for modern servers and any disk larger than 2TB.

2. Tools of the Trade

Linux provides three main tools for the command line:

Tool	Format	User Experience
`fdisk`	MBR (mostly)	Simple, interactive menu.
`gdisk`	GPT	Same interface as fdisk, but for GPT disks.
`parted`	Both	More advanced, one-line commands (good for scripts).

3. Practical: The Safe Disk Inspection

Before you edit a disk, you must identify its "Device Name."

# List all disks and their partitions
lsblk

# See the detailed partition table of a specific disk
sudo fdisk -l /dev/sda

CAUTION: In Linux, your disks are usually named /dev/sda, /dev/sdb, etc. On modern NVMe SSDs, they look like /dev/nvme0n1.

4. Creating a New Partition (Interactive)

Let's imagine we added a second hard drive /dev/sdb. We want to use it for data.

sudo gdisk /dev/sdb

The Workflow:

Type o to create a new empty GPT table (Warning: Wipes the disk!).
Type n for a new partition.
Accept the defaults for Partition Number and First Sector.
For Last Sector, type +100G (to make a 100GB partition).
For Hex Code, use 8300 (Linux Filesystem).
Type w to Write changes to the disk and exit.

5. The "Kernel Panic": Informing the OS

Sometimes, you create a partition but lsblk doesn't show it yet. This is because the Kernel is still using the "Old Map" in its memory. You must force it to re-read the disk.

# Force the kernel to re-read partition tables
sudo partprobe /dev/sdb

6. Example: A Disk Layout Auditor (Python)

If you are managing a fleet of servers, you want to ensure they all use GPT and have at least 10% unallocated space for future LVM expansion. Here is a Python script that audits the partition format.

import subprocess
import json

def audit_disk_format():
    """
    Uses lsblk in JSON mode to check partition labels.
    """
    print("--- Disk Label Audit ---")
    print("-" * 30)
    
    try:
        # Get disk info in JSON format
        res = subprocess.run(['lsblk', '-J', '-o', 'NAME,PTTYPE,SIZE'], capture_output=True, text=True)
        data = json.loads(res.stdout)
        
        for device in data.get('blockdevices', []):
            name = device['name']
            pttype = device.get('pttype', 'Unknown')
            size = device['size']
            
            if pttype == 'gpt':
                print(f"[OK] {name} ({size}): Using modern GPT format.")
            elif pttype == 'dos':
                print(f"[WA] {name} ({size}): Using legacy MBR (dos) format.")
            else:
                print(f"[??] {name} ({size}): No partition table detected.")
                
    except Exception as e:
        print(f"Error auditing disks: {e}")

if __name__ == "__main__":
    audit_disk_format()

7. Professional Tip: Align Your Sectors

Older tools started partitions at Sector 63. Modern 4K-sector drives perform significantly better if the partition starts at an "Even" number (usually Sector 2048). fdisk and gdisk now do this automatically, but if you are using manually-calculated offsets in a script, always align to 1MiB (2048 sectors).

8. Summary

Partitioning is the physical organization of your storage.

GPT is the modern standard for safety and large disks.
lsblk is the best way to see your "Storage Tree."
gdisk is the preferred interactive tool for GPT systems.
partprobe is necessary if the OS doesn't see your new partitions immediately.

Now that we have the "Rooms" built, we need to lay down the "Flooring" so we can store files. In the next lesson, we will look at Creating and Mounting Filesystems (ext4, XFS, Btrfs).

Quiz Questions

Why is GPT safer than MBR in the event of hardware corruption?
What happens if you run gdisk on a disk that already has data and type 'o'?
How can you tell if a disk is using an MBR or a GPT blueprint without editing it?

Continue to Lesson 2: Creating and Mounting Filesystems—ext4, XFS, and Btrfs.

The Skeleton of the Disk: Partitioning, MBR, and GPT