Understanding RAID: Types, Benefits, and a Hands‑On Linux Setup

1. RAID Overview

RAID (Redundant Arrays of Independent Disks) is a disk array technology that combines multiple independent disks into a single logical unit to improve performance, capacity, and fault tolerance through redundancy.

RAID Levels

RAID 0 (Striping, 100% utilization)

Minimum 2 disks

Data is striped across disks

No redundancy – highest performance but no fault tolerance

RAID 1 (Mirroring, 50% utilization)

Minimum 2 disks

Exact copy of data on each disk (mirroring)

Improves read performance and provides high data safety

Highest cost per usable GB

RAID 5 (Block-level striping with distributed parity, (N‑1)/N utilization)

Minimum 3 disks (commonly 4 disks with 1 parity)

Data and parity are striped across all disks

Good read performance; write performance reduced due to parity calculations

Can tolerate a single disk failure

RAID 6 (Double parity, (N‑2)/N utilization)

Minimum 4 disks

Two parity blocks allow tolerance of two simultaneous disk failures

Write performance lower than RAID 5

RAID 1+0 (Mirrored stripes)

Minimum 4 disks

Creates two RAID 0 sets and mirrors each pair (RAID 1)

Combines redundancy and performance; widely used in practice

2. Core RAID Concepts

Striping

Striping splits data into equal-sized blocks and distributes them across multiple disks, increasing I/O concurrency and throughput.

Mirroring

Mirroring duplicates data on two or more disks, enhancing reliability and allowing parallel reads, though writes are slower due to duplication.

Parity (Data Check)

Parity uses redundant data (e.g., XOR calculations) to detect and correct errors, improving fault tolerance at the cost of additional read/write overhead.

3. Common Storage Interfaces

IDE (Integrated Drive Electronics) : Parallel interface, low cost, high compatibility.

SCSI (Small Computer System Interface) : High‑speed, multi‑tasking, supports hot‑swap; more expensive, used in servers and workstations.

SATA (Serial ATA) : Serial interface with up to 6 Gb/s (SATA 2.0) and 12 Gb/s (SATA 3.0) rates.

SAS (Serial Attached SCSI) : Successor to SCSI, uses serial signaling, compatible with SATA devices.

4. RAID Experiment Configuration (Linux)

mdadm -Cv /dev/md5 -n3 -l5 /dev/sd[b-d]1 -x1 /dev/sde1   # create RAID5 with 3 data disks + 1 spare

mkfs.xfs /dev/md5

mkdir /opt/md5

mount /dev/md5 /opt/md5

touch /opt/md5/test{1..66}.txt   # generate test files