What does RAID stand for?
RAID stands for Redundant Array of Independent Disks. Combining several drives into one logical volume for speed, redundancy or both. RAID 0 stripes with no redundancy, 1 mirrors, 5 stripes with parity (three drives minimum, survives one failure), 10 mirrors then stripes. RAID is not a backup.
RAID combines several drives so that they behave as one volume, to gain speed, to survive a drive failure, or both. RAID 0 stripes data across drives for speed and has no redundancy: one failed drive loses everything. RAID 1 mirrors the same data on two drives. RAID 5 stripes data with parity across at least three drives and survives one failure. RAID 6 uses double parity across at least four drives and survives two. RAID 10 stripes across mirrored pairs and needs at least four drives.
RAID in practice: an example
A small file server has four 4 TB drives in RAID 5. One drive fails on Friday night. The volume stays online, more slowly, and about 12 TB remain usable because one drive's worth of space holds parity. The technician replaces the failed drive on Monday and the array rebuilds onto it.
What RAID is confused with
RAID vs backup: what is the difference?
RAID protects against a drive failing. It does not protect against deleted files, ransomware, a fire or a failed controller, because every drive in the array receives the same change. A backup is a separate copy.
RAID vs AHCI: what is the difference?
AHCI and RAID are both modes of the storage controller in firmware setup. In AHCI mode each drive is presented individually; in RAID mode the controller can combine drives into arrays.
Which exams cover RAID?
RAID is on the official CompTIA acronym list for one of the four exams covered here.
- A+ 220-1201 and 220-1202: 220-1201 3.0 (Hardware); 220-1201 5.0 (Hardware and Network Troubleshooting).
Each number is a CompTIA exam objective and the name in brackets is its domain. The exam puts the term in a scenario; it does not ask you to recite the expansion.
Check yourself: two practice questions
Written by CertSprint for this page. They are not taken from any exam.
1. A workstation needs the fastest possible scratch volume from two drives, and losing the data would not matter. Which level fits?
- RAID 0
- RAID 1
- RAID 5
- RAID 6
Show the answer
A. RAID 0. Striping uses the full capacity of both drives and gives the best speed, at the price of no redundancy. RAID 5 and 6 need more drives and RAID 1 gives no speed gain for writes.
2. A server must stay online if any two drives fail at the same time. Which level guarantees that?
- RAID 0
- RAID 1 with two drives
- RAID 5
- RAID 6
Show the answer
D. RAID 6. Double parity lets RAID 6 lose any two drives. RAID 5 survives one, a two-drive mirror survives one, and RAID 0 survives none.
Sources: NIST glossary: redundant array of independent disks; NIST SP 800-34 Rev. 1, Contingency Planning Guide for Federal Information Systems; Microsoft Learn: Fault tolerance and storage efficiency (mirroring and parity). The acronym and its expansion come from CompTIA's official acronym lists, linked from each exam glossary above. The explanation, example and questions are CertSprint's own, checked against these sources on 11 November 2026.