If you’re preparing for the CompTIA A+ Core 1 exam (220-1201), understanding RAID levels is non-negotiable. RAID — which stands for Redundant Array of Independent Disks — shows up in the Hardware domain, which makes up a hefty 25% of the Core 1 exam. You’ll need to know not just what each RAID level is, but when and why you’d choose one over another. Let’s break this down properly so you walk into the exam confident — not guessing.
What Is RAID and Why Does It Matter?
RAID is a storage technology that combines multiple physical drives into a single logical unit. Depending on the configuration, RAID can improve performance, provide fault tolerance (the ability to survive a drive failure), or both. System administrators and IT technicians use RAID constantly in servers, workstations, and NAS (Network Attached Storage) devices.
The CompTIA A+ exam expects you to understand the trade-offs of each RAID level — specifically around speed, redundancy, storage efficiency, and minimum disk requirements. There are four RAID levels you absolutely must know: RAID 0, RAID 1, RAID 5, and RAID 10.
RAID 0: Speed Without Safety
RAID 0 is often called striping. Data is split across two or more drives simultaneously, which means read and write speeds are significantly faster than a single drive. Think of it like two lanes on a highway instead of one — traffic moves faster because it’s divided.
- Minimum drives required: 2
- Fault tolerance: None — if one drive fails, all data is lost
- Storage efficiency: 100% of total capacity is usable
- Best for: High-performance use cases where data loss is acceptable (e.g., video editing scratch disks, gaming)
The critical exam takeaway: RAID 0 offers no redundancy whatsoever. It’s the fastest, but the riskiest. If a question describes a scenario where speed is the priority and data protection isn’t a concern, RAID 0 is your answer.
RAID 1: Redundancy Without Compromise
RAID 1 is called mirroring. Every piece of data written to one drive is simultaneously written to a second drive — an exact mirror image. If one drive dies, the other continues operating without interruption.
- Minimum drives required: 2
- Fault tolerance: Yes — survives one drive failure
- Storage efficiency: 50% (you lose half your total capacity to mirroring)
- Best for: Critical data where uptime matters — operating system drives, financial records, databases
The trade-off here is cost and capacity. You’re paying for double the drives but only getting half the usable storage. The exam may present scenarios asking which RAID level is best for data protection with only two drives — that’s RAID 1.
RAID 5: The Balanced Option
RAID 5 uses a technique called striping with parity. Data is striped across three or more drives, but a parity block is also distributed across all drives. This parity data allows the system to reconstruct data if a single drive fails — without needing a full duplicate drive like RAID 1 does.
- Minimum drives required: 3
- Fault tolerance: Yes — survives one drive failure
- Storage efficiency: You lose the equivalent of one drive to parity (e.g., 3 drives = 2 drives of usable space)
- Best for: File servers, general-purpose business storage, when you need a balance of performance, capacity, and redundancy
RAID 5 is the most commonly tested middle-ground option. The exam will often describe a scenario where a business needs fault tolerance without sacrificing too much storage capacity — and RAID 5 is the right answer. Know that it requires a minimum of three drives and can tolerate the failure of exactly one drive.
RAID 10: The Best of Both Worlds (At a Price)
RAID 10 (also written as RAID 1+0) combines mirroring and striping. You’re essentially mirroring your data first (RAID 1), then striping across those mirrored pairs (RAID 0). This gives you both high performance and strong fault tolerance.
- Minimum drives required: 4
- Fault tolerance: Yes — can survive multiple drive failures as long as they don’t occur in the same mirrored pair
- Storage efficiency: 50% (same as RAID 1, because mirroring is still happening)
- Best for: High-performance databases, virtualization hosts, enterprise applications
RAID 10 is expensive — you need at least four drives and only use half the total capacity — but it’s the top performer with redundancy built in. If the exam describes a scenario that demands both speed and fault tolerance and cost isn’t a constraint, RAID 10 is your answer.
Quick Comparison: RAID Levels at a Glance
- RAID 0: Striping | 2+ drives | No fault tolerance | 100% capacity | Fast
- RAID 1: Mirroring | 2+ drives | 1 drive failure | 50% capacity | Reliable
- RAID 5: Striping with parity | 3+ drives | 1 drive failure | (n-1) capacity | Balanced
- RAID 10: Mirror + Stripe | 4+ drives | Multiple failures (not same pair) | 50% capacity | Fast + Reliable
Test Your Knowledge
Let’s put your understanding to the test with a couple of exam-style questions.
Question 1: A technician is setting up a storage system for a video production company. They need maximum read/write performance and have no concern about data loss since files are backed up nightly to the cloud. Which RAID level should the technician implement?
- RAID 1
- RAID 5
- RAID 0
- RAID 10
Answer: C — RAID 0. The scenario prioritizes performance over data protection, and an external backup mitigates the risk of drive failure. RAID 0 provides maximum speed with 100% usable capacity, making it the right fit here.
Question 2: A small business wants to protect its file server from a single drive failure while making efficient use of three available drives. Which RAID level is most appropriate?
- RAID 0
- RAID 1
- RAID 10
- RAID 5
Answer: D — RAID 5. With exactly three drives, RAID 5 provides fault tolerance against one drive failure and maximizes usable storage by only sacrificing the equivalent of one drive to parity. RAID 10 requires four drives minimum, and RAID 1 would waste too much capacity.
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Study Tips for RAID on the CompTIA A+ Exam
- Focus on scenario-based questions. The 220-1201 exam rarely asks “what is RAID 5?” directly. Instead, it presents a business scenario and asks you to choose the best solution. Practice identifying which RAID level fits the described need.
- Memorize the minimum drive counts. RAID 0 and 1 need 2, RAID 5 needs 3, RAID 10 needs 4. These are quick points you don’t want to lose on exam day.
- Know the failure tolerance of each level. RAID 0 = zero tolerance. RAID 1 and 5 = one drive. RAID 10 = potentially multiple, depending on which drives fail.
- Connect concepts to real IT work. Ask yourself: where would I actually use this? Servers use RAID 5 or 10. Home enthusiasts might use RAID 0 or 1. That context helps the information stick.
Frequently Asked Questions
Which RAID level does the CompTIA A+ exam focus on most?
The 220-1201 Core 1 exam tests all four common RAID levels — 0, 1, 5, and 10 — but scenario-based questions about RAID 5 and RAID 10 tend to appear frequently because they require understanding trade-offs between performance, redundancy, and cost. Don’t skip any of them.
Is RAID a replacement for backups?
No — and this is an important distinction for both the exam and real-world IT work. RAID provides fault tolerance against drive failure, but it does not protect against accidental deletion, ransomware, or catastrophic hardware failure. Backups and RAID serve different purposes and should be used together.
What domain covers RAID on the CompTIA A+ Core 1 exam?
RAID falls under the Hardware domain (Domain 3) of the Core 1 exam (220-1201), which accounts for 25% of the total exam. This is one of the largest domains, so it’s worth spending significant study time here. Topics include motherboards, CPUs, RAM, storage, and peripherals alongside RAID configurations.
How many drives do I need for each RAID level?
RAID 0 and RAID 1 each require a minimum of 2 drives. RAID 5 requires a minimum of 3 drives. RAID 10 requires a minimum of 4 drives. These minimums are commonly tested on the exam, so commit them to memory — they’re quick and reliable points.
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