Understanding RAID: Types, Benefits, and Practical Configuration

1. RAID

RAID (Redundant Arrays of Independent Disks) is a group of independent disks combined into a large array that uses redundancy to improve performance and reliability.

RAID0 (Utilization: 100%)

Requires at least two disks; data is striped across disks; no redundancy; highest performance but no fault tolerance; unsuitable for high‑safety requirements.

RAID1 (Utilization: 50%)

Requires at least two disks; provides data mirroring for redundancy; good read performance; when one disk fails, the system switches to the mirror without data loss.

RAID5 (Utilization: (N‑1)/N)

Minimum three disks; data is striped with distributed parity; balances performance and redundancy; suitable for read‑heavy workloads; write performance is lower due to parity calculations.

RAID6 (Utilization: (N‑2)/N)

Requires at least four disks; adds a second parity block, allowing two simultaneous disk failures without data loss; write performance is poorer than RAID5.

RAID1+0

Minimum four disks; first creates two RAID0 stripes, then mirrors each stripe (RAID1); combines redundancy and performance; commonly used in practice.

2. RAID Techniques and Concepts

Striping divides continuous data into equal‑sized blocks and writes each block to a different disk, effectively merging multiple drives into a single volume.

Mirroring

Copies data to multiple disks, improving reliability and allowing concurrent reads from replicas; write performance is slightly reduced due to the need to write to all copies.

Data Striping

Distributes data fragments across several disks, increasing I/O concurrency and overall throughput; differs from mirroring, which creates full copies.

Data Parity

Uses redundant information (e.g., XOR, Hamming code) to detect and correct errors; enhances reliability but adds CPU and I/O overhead.

Different RAID levels combine one or more of these techniques to achieve desired trade‑offs among reliability, availability, and performance.

3. Storage Interface Cards

IDE (Integrated Drive Electronics) integrates the controller with the drive; offers low cost and strong compatibility, using a parallel interface.

SCSI (Small Computer System Interface) is a high‑speed, multi‑tasking interface used mainly in servers and workstations; provides high bandwidth and hot‑swap capability but at higher cost.

SATA (Serial ATA) uses serial transmission; SATA 2.0 reaches up to 3 Gb/s, while SATA 3.0 can reach 6 Gb/s.

SAS (Serial Attached SCSI) is the successor to SCSI, using serial technology like SATA and is backward compatible with SATA drives.

4. RAID Experiment Configuration

mdadm -Cv /dev/md5 -n3 -l5 /dev/sd[b-d]1 -x1 /dev/sde1   # create RAID5
mkfs.xfs /dev/md5
mkdir /opt/md5
mount /dev/md5 /opt/md5   # mount the array
touch /opt/md5/test{1..66}.txt   # create test files