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TEC-DATA82-06 · Lesson 4 · 10 clock hours · lab

RAID Configuration and Storage Subsystems

Objective. Students will create RAID 1 and RAID 5 virtual disks using a hardware RAID controller utility, explain the fault-tolerance and capacity trade-offs of each level, and simulate a drive failure and rebuild.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by an industry-certified professional or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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What Is RAID?

RAID stands for Redundant Array of Independent Disks. A RAID system combines multiple physical drives so that the server sees one or more logical storage units called virtual disks. Depending on the RAID level chosen, the array can improve read/write performance, protect data against drive failure, or do both. In data centers, RAID is a standard layer of protection beneath the operating system and above the physical drives.

Hardware RAID vs. Software RAID

A hardware RAID controller is a dedicated card (or chipset built into a server board) that manages all RAID operations independently of the CPU and operating system. The OS sees only the virtual disk, not the individual drives. Hardware controllers maintain a battery-backed or flash-backed cache, which improves write performance and protects in-flight data during a power interruption. Software RAID uses the OS and CPU instead; it costs less but adds CPU overhead and offers no cache protection. Data centers almost always use hardware RAID controllers.

Common RAID Levels

RAID 0 — Striping, No Redundancy

Data is split in blocks (stripes) across all drives. All drive capacity is usable, and read/write throughput is high. However, if any single drive fails, all data is lost. RAID 0 is used only where speed matters and data loss is acceptable (scratch storage, rendering caches).

RAID 1 — Mirroring

Data is written identically to two drives simultaneously. Usable capacity equals the size of one drive regardless of how many drives are in the mirror set. The array survives the failure of all but one drive. Read performance may improve because the controller can service reads from either drive. Write speed is limited to the slower of the two drives. RAID 1 is common for operating system volumes.

RAID 5 — Striping with Distributed Parity

Data and parity information are striped across all drives. Parity is distributed—no single drive holds all parity. With n drives, usable capacity equals (n − 1) × drive size. The array tolerates one drive failure; the missing data is reconstructed from parity. RAID 5 requires a minimum of three drives. It balances capacity efficiency and fault tolerance and is widely used for application data volumes.

RAID 6 — Striping with Double Distributed Parity

Similar to RAID 5 but with two independent parity calculations per stripe. Usable capacity equals (n − 2) × drive size. The array tolerates two simultaneous drive failures. Minimum four drives required. RAID 6 is preferred when drives are large and rebuild times are long, because a second failure during rebuild is a real risk with large-capacity drives.

Fault Tolerance and Capacity Trade-offs

| Level | Min Drives | Drives Tolerated Lost | Usable Capacity |

|-------|-----------|----------------------|------------------|

| RAID 0 | 2 | 0 | n × size |

| RAID 1 | 2 | n − 1 | 1 × size |

| RAID 5 | 3 | 1 | (n − 1) × size |

| RAID 6 | 4 | 2 | (n − 2) × size |

Always match the RAID level to the workload. High-transaction databases often use RAID 10 (mirrored stripes). Boot volumes use RAID 1. Large sequential workloads use RAID 5 or 6.

Using the Hardware RAID Controller Utility

Most enterprise RAID controllers provide a utility accessible at server POST (commonly by pressing a key combination such as CTRL+R for Dell PERC controllers, or through a browser-based interface). Steps are broadly:

1. Enter the controller configuration utility.

2. Select physical drives and choose a RAID level.

3. Set stripe size (common choices: 64 KB for general use, 256 KB for large sequential files).

4. Name the virtual disk and confirm creation.

5. Allow initialization to complete (fast init marks the disk available immediately; full init writes zeros and takes longer).

Always verify the virtual disk properties after creation: capacity, stripe size, and RAID level should match your design.

Simulating a Drive Failure and Rebuild

Enterprise RAID controllers support hot-swap: drives can be removed and replaced while the server stays powered. When a drive is removed from a RAID 5 or RAID 6 array, the controller immediately marks the virtual disk degraded. In degraded state:

When a replacement drive is inserted, the controller begins a rebuild. Rebuild time depends on drive capacity and the load on the array. The controller event log records the failure, the degraded state, the start of rebuild, and completion. Documenting these log entries is a required skill for CompTIA Server+ and for real-world incident reporting.

Safety Points

Electrical safety: Before working inside any server chassis, follow your facility's lockout/tagout (LOTO) procedure to de-energize equipment unless the task specifically requires the system to be powered (as in a hot-swap exercise). Hot-swap drive replacement is designed to be done with power on, but keep hands clear of fan modules and power supplies.

ESD (Electrostatic Discharge): Always wear an anti-static wrist strap bonded to the server chassis ground, or use an ESD mat. Physical drives contain sensitive electronics that can be destroyed by static discharge that you cannot feel.

PPE: Safety glasses are not required for this specific task, but closed-toe shoes are required in any server room per standard facility rules. Follow your site's PPE policy.

Lifting: Servers and drive trays can be heavy. Use two-person lifts for chassis weighing more than 35 lb, and use a server lift cart when racking equipment.

Key terms8

Virtual DiskThe logical storage unit presented to the operating system by a RAID controller, created from one or more physical drives combined according to a RAID level.
Stripe SizeThe amount of data written to each drive before the controller moves to the next drive in the array; also called chunk size. Affects performance for different workload types.
ParityCalculated redundancy data derived from the actual data stripes; used by RAID 5 and RAID 6 to reconstruct lost data when a drive fails.
Hot-SwapThe ability to remove and replace a drive while the server remains powered and operational, without interrupting service.
Degraded ModeThe operating state of a RAID array after one or more drives fail but before the lost data is fully rebuilt; the array still functions but has reduced or eliminated fault tolerance.
RebuildThe process by which the RAID controller reconstructs lost data from the remaining drives onto a replacement drive after a failure.
Hardware RAID ControllerA dedicated card or chipset that manages RAID operations independently of the server CPU and OS, typically including a battery- or flash-backed write cache.
RAID 6A RAID level that uses two independent sets of distributed parity, tolerating up to two simultaneous drive failures; usable capacity is (n − 2) drive sizes.

Worked examples4

1. You have four 2 TB drives and create a RAID 5 array. What is the usable capacity?
  1. Identify the formula for RAID 5 usable capacity: (n − 1) × drive size, where n = number of drives.
  2. Substitute values: n = 4, drive size = 2 TB.
  3. (4 − 1) × 2 TB = 3 × 2 TB.
Answer: 6 TB usable capacity. One drive's worth (2 TB) is used for parity.
2. You have six 4 TB drives and create a RAID 6 array. What is the usable capacity, and how many drives can fail simultaneously without data loss?
  1. Identify the RAID 6 formula: usable capacity = (n − 2) × drive size; drives tolerated = 2.
  2. Substitute values: n = 6, drive size = 4 TB.
  3. (6 − 2) × 4 TB = 4 × 4 TB = 16 TB.
  4. RAID 6 always tolerates exactly 2 simultaneous drive failures regardless of n.
Answer: 16 TB usable capacity; up to 2 drives can fail simultaneously without data loss.
3. You have two 1 TB drives in a RAID 1 mirror. A third 1 TB drive is added to expand the mirror. What is the usable capacity of the resulting three-drive RAID 1?
  1. RAID 1 usable capacity is always equal to the capacity of a single drive, regardless of how many drives are in the mirror set.
  2. All three drives store identical data.
  3. Usable capacity = 1 × 1 TB = 1 TB.
Answer: 1 TB usable capacity. Adding more drives to a RAID 1 increases redundancy but does not increase usable capacity.
4. A RAID 5 array uses five 6 TB drives. After one drive fails and is replaced, the controller estimates a rebuild rate of roughly 50 GB per hour (a conservative real-world figure for a loaded array). Approximately how many hours will the rebuild take?
  1. Usable data that must be reconstructed is spread across the remaining four drives. The controller must read all remaining data and parity to regenerate the missing drive's content; the data to be written to the new drive equals one drive's worth: 6 TB.
  2. Convert 6 TB to GB: 6 × 1024 GB = 6,144 GB.
  3. Divide by rebuild rate: 6,144 GB ÷ 50 GB/hr ≈ 122.9 hours.
  4. Round to a practical estimate.
Answer: Approximately 123 hours (about 5 days) at 50 GB/hr. This illustrates why large drives and heavy load make RAID 6 (two-failure tolerance) preferable over RAID 5 for high-capacity arrays.

The math in this lesson1

Learners compute RAID 5 usable capacity as (n − 1) times drive size.
A-SSE.1
Brush up in the math halls at newSchoolWorks.com:
In class: Lecture and whiteboard session: instructor draws RAID 0, 1, 5, and 6 stripe/mirror maps; students calculate usable capacity and number of tolerated drive failures for each scenario using a provided worksheet. · Hands-on RAID controller utility (e.g., CTRL+R or browser-based RAID manager): students create a RAID 1 pair, note the virtual disk properties, then create a separate RAID 5 array across four drives. · Simulated drive failure: instructor hot-pulls one drive from the RAID 5 array; students observe degraded status in the controller log, re-insert a spare, initiate a rebuild, and document the rebuild time estimate and event log entries.
Materials: Servers with hardware RAID controllers and at least six identical drives, RAID controller utility access, RAID calculation worksheets, CompTIA Server+ study guide (storage domain), lab documentation forms
Check: Both RAID arrays created with correct properties (capacity, stripe size); drive failure and rebuild documented accurately with event log screenshot or printout—pass requires correct arrays and complete documentation.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

CompTIA Server+ — Storage
1. A RAID 5 array is built from five 8 TB drives. What is the usable capacity?
CompTIA Server+ — Storage
2. Which RAID level provides fault tolerance while using the least amount of raw capacity for redundancy when exactly two drives are available?
CompTIA Server+ — Storage
3. During the lab, the instructor hot-pulls one drive from a RAID 5 array. What status does the controller immediately report for the virtual disk?
CompTIA Server+ — Storage
4. What is the MINIMUM number of physical drives required to create a RAID 6 array?
OSHA 10 / CNet CDCTP — Safety
5. A technician is replacing a failed hot-swap drive in a running server. Which safety measure is MOST important before touching the drive tray?
CompTIA A+ — Storage
6. Which RAID level stripes data across all drives with NO parity or mirroring, offering maximum write speed but zero fault tolerance?
CompTIA Server+ — Storage
7. A RAID 5 array is in degraded mode after a drive failure. A technician inserts a replacement drive and the controller begins a rebuild. Compared to normal operation, how does array READ performance typically behave during the rebuild?
CompTIA Server+ — Storage
8. A storage administrator wants an array that can survive TWO simultaneous drive failures and has six 10 TB drives available. Which RAID level should be chosen, and what will the usable capacity be?
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