1.2 Given a scenario, deploy and manage storage.
📘CompTIA Server+ (SK0-005)
This section explains RAID levels and types in simple, clear language. It is written for exam preparation and for learners who may be new to IT, while still covering everything required for the Server+ (SK0-005) exam.
What Is RAID?
RAID (Redundant Array of Independent Disks) is a way of combining multiple physical hard drives into one logical storage unit. RAID is used to:
- Improve performance (speed)
- Improve fault tolerance (disk failure protection)
- Increase storage capacity
- Balance speed, redundancy, and cost
A RAID setup is commonly found in:
- File servers
- Database servers
- Virtualization hosts
- Application servers
Important exam note: RAID is not a backup. RAID protects against disk failure, not accidental deletion, malware, or data corruption.
RAID 0 (Striping)
How RAID 0 Works
- Data is split (striped) across two or more disks
- Each disk stores part of the data
- No duplication of data
Minimum Disks Required
- 2 disks
Key Characteristics
- Very fast performance
- No fault tolerance
- Maximum usable capacity
If one disk fails, all data is lost.
Advantages
- Excellent read and write speed
- Full disk capacity is usable
Disadvantages
- No data protection
- High risk of data loss
Exam Focus
- RAID 0 = Performance only
- No redundancy
- Used where speed is more important than data safety
RAID 1 (Mirroring)
How RAID 1 Works
- Data is copied exactly to two disks
- Each disk contains the same data
Minimum Disks Required
- 2 disks
Key Characteristics
- High fault tolerance
- Slower write performance than RAID 0
- Only 50% usable capacity
If one disk fails, the system continues running using the other disk.
Advantages
- Simple and reliable
- Easy recovery after disk failure
Disadvantages
- High storage cost (half the space is lost)
Exam Focus
- RAID 1 = Redundancy through mirroring
- Common for OS disks and critical system volumes
RAID 5 (Striping with Distributed Parity)
How RAID 5 Works
- Data is striped across multiple disks
- Parity information is distributed across all disks
- Parity allows recovery if one disk fails
Minimum Disks Required
- 3 disks
Key Characteristics
- Can tolerate one disk failure
- Good balance of performance and redundancy
- Write performance is slower due to parity calculation
Advantages
- Efficient use of disk space
- Fault tolerance with good read speed
Disadvantages
- Slow rebuild times
- Poor performance during rebuild
- Risky with very large disks
Exam Focus
- RAID 5 = 1 disk fault tolerance
- Popular in file and application servers
RAID 6 (Striping with Double Parity)
How RAID 6 Works
- Similar to RAID 5
- Uses two sets of parity data
- Can survive two disk failures
Minimum Disks Required
- 4 disks
Key Characteristics
- High fault tolerance
- Slower write performance than RAID 5
- Safer for large-capacity disks
Advantages
- Can survive two simultaneous disk failures
- Better reliability than RAID 5
Disadvantages
- More disk space used for parity
- Slower write speed
Exam Focus
- RAID 6 = 2 disk fault tolerance
- Used in environments where uptime is critical
RAID 10 (1+0 – Mirrored Stripes)
How RAID 10 Works
- Combines RAID 1 and RAID 0
- Disks are mirrored, then striped
Minimum Disks Required
- 4 disks
Key Characteristics
- High performance
- High fault tolerance
- Expensive due to disk usage
Can tolerate multiple disk failures as long as they are not in the same mirror set.
Advantages
- Fast reads and writes
- Quick rebuild times
- Very reliable
Disadvantages
- High cost
- Only 50% usable capacity
Exam Focus
- RAID 10 = Best performance + redundancy
- Preferred for databases and virtualization
JBOD (Just a Bunch of Disks)
How JBOD Works
- Disks are grouped together
- No striping, no mirroring, no parity
- Each disk operates independently
Minimum Disks Required
- 1 or more disks
Key Characteristics
- No performance improvement
- No fault tolerance
- Simple storage expansion
Advantages
- Full use of disk capacity
- Easy to configure
Disadvantages
- No protection from disk failure
Exam Focus
- JBOD is not RAID
- Used when flexibility and capacity matter more than performance or redundancy
Hardware RAID vs Software RAID
Hardware RAID
Managed by a dedicated RAID controller
Characteristics
- RAID logic handled by hardware
- Independent of operating system
- Often includes cache and battery backup
Advantages
- Better performance
- Lower CPU usage
- More reliable
Disadvantages
- Higher cost
- Controller failure can cause recovery issues
Exam Focus
- Preferred in enterprise environments
Software RAID
Managed by the operating system
Characteristics
- Uses system CPU
- OS-dependent
- Easier to configure
Advantages
- No extra hardware cost
- Flexible
Disadvantages
- Lower performance
- Higher CPU usage
Exam Focus
- Common in small servers and lab environments
Quick Exam Comparison Table (Conceptual)
- RAID 0: Speed only, no protection
- RAID 1: Mirroring, high redundancy
- RAID 5: 1 disk fault tolerance
- RAID 6: 2 disk fault tolerance
- RAID 10: Best performance + redundancy
- JBOD: No RAID features
Key Exam Reminders
- RAID ≠ Backup
- Know minimum disk requirements
- Understand fault tolerance levels
- Recognize use cases in IT environments
- Be able to choose the right RAID level for a scenario
