Filesystem & Storage

1. What is Filesystem in Linux?

A filesystem defines how data is stored, organized, and accessed on storage devices.

👉 Think:

• Disk = raw storage

• Filesystem = structure + rules to store files

Examples:

• ext4 (most common in Linux)

• xfs (used in enterprise, high performance)

• btrfs (advanced features like snapshots)

• tmpfs (in-memory filesystem)

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2. Linux Storage Stack (VERY IMPORTANT)

In interviews, always explain this layered architecture 👇

Application
   ↓
Filesystem (ext4, xfs)
   ↓
VFS (Virtual File System)
   ↓
Block Layer
   ↓
Device Drivers
   ↓
Physical Disk (HDD/SSD/NVMe)

🔥 Key Points:

• VFS (Virtual File System) → abstraction layer
  → allows Linux to support multiple filesystems

• Apps don’t care if it’s ext4, xfs, NFS, etc.

👉 Interview line:

“Linux uses VFS to provide a unified interface across different filesystem types.”

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🗂️ 3. Types of Filesystems (Important)

🔹 Local Filesystems

• ext4 → default, journaling, stable

• xfs → high performance, large files

• btrfs → snapshots, compression

🔹 Network Filesystems

• NFS → share storage across servers

• SMB/CIFS → Windows-compatible sharing

🔹 Virtual / Special

• procfs → process info (/proc)

• sysfs → kernel/device info (/sys)

• tmpfs → RAM-based

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📁 4. Linux Directory Structure (FHS)

Very common question.

Directory	Purpose
/	Root
/home	User data
/var	Logs, dynamic data
/etc	Config files
/bin, /usr/bin	Binaries
/dev	Devices
/proc	Process info

👉 Interview tip:

“Linux follows FHS (Filesystem Hierarchy Standard) to maintain consistency.”

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💽 5. Storage Concepts (CORE DEVOPS PART)

🔹 Partitioning

Splitting disk into parts.

Commands:

fdisk
parted
lsblk

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🔹 Mounting

Linux doesn’t auto-use disks → you must mount.

mount /dev/sdb1 /mnt/data

Persistent mount:

/etc/fstab

👉 Critical interview point:

“Everything in Linux is mounted under root / — unlike Windows drives.”

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🔹 Inodes (VERY IMPORTANT)

Each file has an inode containing:

• metadata

• permissions

• size

• pointers to data blocks

👉 NOT filename (that’s stored in directory)

Check:

ls -i
df -i

👉 Interview trap:

Disk can have free space but still fail if inodes are exhausted.

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🔹 Journaling

Used in ext4, xfs

👉 Prevents corruption during crashes
→ logs changes before writing

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⚙️ 6. LVM (Logical Volume Manager) 🔥🔥

VERY IMPORTANT for DevOps

Allows flexible storage management.

Structure:

Disk → PV → VG → LV → Filesystem

• PV → Physical Volume

• VG → Volume Group

• LV → Logical Volume

Benefits:

• Resize storage without downtime

• Combine multiple disks

• Snapshots

Commands:

pvcreate
vgcreate
lvcreate
lvextend

👉 Interview line:

“LVM abstracts physical storage and provides dynamic resizing and snapshots.”

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⚡ 7. RAID (Redundant Array of Disks)

Used for:

• performance

• redundancy

Types:

RAID	Use Case
RAID 0	Fast, no redundancy
RAID 1	Mirroring
RAID 5	Parity
RAID 10	Best combo

👉 DevOps context:

• Used in servers, cloud disks internally

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📊 8. Disk Monitoring & Commands

Must-know commands:

df -h  # disk usage
du -sh # folder size
lsblk  # block devices
mount  # mounted disks
blkid  # UUIDs

Advanced:

iostat
iotop

👉 Interview tip:

Always mention monitoring + troubleshooting

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🚀 9. Performance Concepts

• SSD vs HDD vs NVMe

• IOPS (Input/Output ops per second)

• Throughput vs latency

👉 Example:

• DB → needs high IOPS

• Logs → sequential writes

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☁️ 10. Cloud + DevOps Context (IMPORTANT)

AWS Example:

• EBS → block storage

• S3 → object storage

• EFS → network filesystem

Kubernetes:

• Persistent Volumes (PV)

• Persistent Volume Claims (PVC)

👉 Interview line:

“Kubernetes abstracts storage using PV/PVC similar to how LVM abstracts disks.”

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🔥 11. Real Interview Scenarios

❓ Disk full but df shows space?

• inode exhaustion

• deleted file still open

❓ How to extend disk?

• add disk → LVM → resize → resize2fs

❓ Logs filling disk?

• /var/log cleanup

• logrotate

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🧠 12. Pro-Level Insights (This makes you stand out)

• xfs cannot shrink, only grow

• ext4 supports both grow + shrink

• tmpfs uses RAM → super fast

• noatime mount option → improves performance

• UUID vs device names in /etc/fstab

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🎯 How to Answer in Interview (Perfect Structure)

If asked:

👉 “Explain Linux filesystem”

Answer flow:

1. Definition

2. Storage stack (VFS)

3. Types (ext4, xfs…)

4. Mounting + FHS

5. Inodes

6. LVM

7. Real-world usage

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