Guide: Managing Storage

RAID Overview

Redundant Array of Independent Disks (RAID) combines multiple physical drives into a single logical unit to improve performance, reliability, or both. This guide walks you through RAID concepts, choosing the right level, setup, monitoring, and troubleshooting.

Common RAID Levels

RAID 0 – Striping

Purpose: Maximize performance.

Pros: High read/write speed, full capacity usage.

Cons: No redundancy – a single disk failure destroys all data.

Typical Use Cases: Scratch disks, temporary storage, non‑critical workloads.

RAID 1 – Mirroring

Purpose: Data protection through duplication.

Pros: Simple redundancy, fast read performance.

Cons: 50% usable capacity, higher cost per GB.

Typical Use Cases: OS drives, critical data, small business servers.

RAID 5 – Striping with Parity

Purpose: Balanced performance and fault tolerance.

Pros: Good read speed, single-disk fault tolerance, efficient storage.

Cons: Write penalty due to parity calculations; rebuild times can be long.

Typical Use Cases: File servers, database read‑heavy workloads.

RAID 6 – Dual Parity

Purpose: Higher fault tolerance (two disk failures).

Pros: Strong data protection, similar capacity efficiency to RAID 5.

Cons: Additional write overhead, longer rebuild.

Typical Use Cases: Large storage arrays, archival systems.

RAID 10 (1+0) – Mirrored Stripes

Purpose: Combine performance of RAID 0 with redundancy of RAID 1.

Pros: Excellent read/write throughput, can survive multiple failures (as long as they’re not in the same mirrored pair).

Cons: 50% usable capacity, requires at least 4 drives.

Typical Use Cases: High‑performance databases, virtualization hosts.

Choosing the Right RAID Level

Performance‑first: RAID 0 or RAID 10.
Data protection: RAID 1, RAID 5, RAID 6, or RAID 10.
Budget constraints: RAID 5 offers a good balance.
Scalability: RAID 6 and RAID 10 scale well with larger arrays.

Step‑by‑Step Setup (Linux mdadm)

# Install mdadm
sudo apt-get update && sudo apt-get install mdadm

# Verify disks (e.g., /dev/sdb, /dev/sdc, /dev/sdd)
lsblk

# Create RAID 5 array
sudo mdadm --create --verbose /dev/md0 \
  --level=5 --raid-devices=3 /dev/sdb /dev/sdc /dev/sdd

# Watch rebuild progress
watch cat /proc/mdstat

# Create filesystem
sudo mkfs.ext4 /dev/md0

# Mount
sudo mkdir -p /mnt/raid
sudo mount /dev/md0 /mnt/raid

# Add to /etc/fstab for persistence
echo '/dev/md0 /mnt/raid ext4 defaults,nofail,discard 0 0' | sudo tee -a /etc/fstab

# Save mdadm config
sudo mdadm --detail --scan | sudo tee -a /etc/mdadm/mdadm.conf
sudo update-initramfs -u

Monitoring & Maintenance

Use cat /proc/mdstat to view array health.
Set up email alerts with mdadm --monitor.
Regularly run smartctl on each drive to catch SMART failures early.
Plan for hot spares: mdadm --add /dev/md0 /dev/sde.
Schedule quarterly scrubs: echo check >/sys/block/md0/md/sync_action.

Frequently Asked Questions

Can I convert RAID 0 to RAID 1 without data loss?

Direct conversion isn’t supported. Back up data, create the new RAID level, and restore.

What is a hot spare?

A standby disk that automatically replaces a failed member, reducing rebuild time.

How many disks can RAID 5 support?

RAID 5 works with 3‑16 disks reliably; beyond that, consider RAID 6 or RAID 10 for better fault tolerance.