first example
This commit is contained in:
Tech08mag
@@ -0,0 +1,359 @@
|
||||
Here's a more detailed summary of the Wikipedia article on **RAID (Redundant Array of Independent Disks)**.
|
||||
|
||||
### What is RAID?
|
||||
|
||||
RAID is a storage virtualization technology that combines multiple physical hard drives or SSDs into one logical storage unit. It was originally designed to improve:
|
||||
|
||||
* **Performance** (faster data access)
|
||||
* **Reliability** (protecting against drive failures)
|
||||
* **Availability** (keeping systems running even when a drive fails)
|
||||
|
||||
Originally, RAID stood for **Redundant Array of Inexpensive Disks**, but it is now commonly referred to as **Redundant Array of Independent Disks**. Data is distributed across drives using different techniques called **RAID levels**, each balancing speed, capacity, and fault tolerance differently. ([Harvey Mudd College][1])
|
||||
|
||||
---
|
||||
|
||||
## History
|
||||
|
||||
RAID was introduced in **1987** by researchers at the University of California, Berkeley. At the time, many small, inexpensive disks could be combined to match or outperform a single large, expensive disk (known as a **SLED – Single Large Expensive Disk**). Over time, RAID became a standard feature in servers, enterprise storage systems, and some desktop computers. ([Harvey Mudd College][1])
|
||||
|
||||
---
|
||||
|
||||
## How RAID Works
|
||||
|
||||
RAID organizes data using three main techniques:
|
||||
|
||||
### 1. Striping
|
||||
|
||||
* Data is divided into blocks.
|
||||
* Blocks are spread across multiple drives.
|
||||
* Increases read and write speed because several drives work simultaneously.
|
||||
|
||||
Example:
|
||||
|
||||
| Disk 1 | Disk 2 |
|
||||
| ------- | ------- |
|
||||
| Block 1 | Block 2 |
|
||||
| Block 3 | Block 4 |
|
||||
| Block 5 | Block 6 |
|
||||
|
||||
---
|
||||
|
||||
### 2. Mirroring
|
||||
|
||||
* Every piece of data is copied onto another drive.
|
||||
* If one drive fails, the copy remains available.
|
||||
|
||||
Example:
|
||||
|
||||
| Disk 1 | Disk 2 |
|
||||
| ------ | ------ |
|
||||
| File A | File A |
|
||||
| File B | File B |
|
||||
|
||||
---
|
||||
|
||||
### 3. Parity
|
||||
|
||||
Parity stores extra information that allows lost data to be reconstructed if a drive fails.
|
||||
|
||||
Instead of storing complete copies like mirroring, RAID calculates parity values from the data blocks.
|
||||
|
||||
Example:
|
||||
|
||||
| Disk 1 | Disk 2 | Disk 3 |
|
||||
| ------ | ------ | ------ |
|
||||
| Data A | Data B | Parity |
|
||||
|
||||
If Disk 1 fails, Data A can be rebuilt using Data B and the parity information.
|
||||
|
||||
Parity is much more storage-efficient than mirroring but requires additional calculations.
|
||||
|
||||
---
|
||||
|
||||
# Standard RAID Levels
|
||||
|
||||
## RAID 0 – Striping
|
||||
|
||||
**Minimum disks:** 2
|
||||
|
||||
Features:
|
||||
|
||||
* Fastest RAID level
|
||||
* No redundancy
|
||||
* Uses 100% of storage capacity
|
||||
|
||||
Advantages:
|
||||
|
||||
* Excellent read/write performance
|
||||
* Full disk capacity available
|
||||
|
||||
Disadvantages:
|
||||
|
||||
* If one disk fails, all data is lost
|
||||
|
||||
Typical use:
|
||||
|
||||
* Gaming
|
||||
* Video editing
|
||||
* Temporary data
|
||||
|
||||
---
|
||||
|
||||
## RAID 1 – Mirroring
|
||||
|
||||
**Minimum disks:** 2
|
||||
|
||||
Features:
|
||||
|
||||
* Every disk has an identical copy.
|
||||
* Very reliable.
|
||||
|
||||
Advantages:
|
||||
|
||||
* Survives one disk failure.
|
||||
* Easy recovery.
|
||||
|
||||
Disadvantages:
|
||||
|
||||
* Only 50% of storage is usable.
|
||||
|
||||
Example:
|
||||
|
||||
Two 2 TB drives become **2 TB usable**, not 4 TB.
|
||||
|
||||
---
|
||||
|
||||
## RAID 2
|
||||
|
||||
Uses bit-level striping with error-correcting codes.
|
||||
|
||||
It is rarely used today because modern drives already perform internal error correction.
|
||||
|
||||
---
|
||||
|
||||
## RAID 3
|
||||
|
||||
Uses:
|
||||
|
||||
* Byte-level striping
|
||||
* One dedicated parity disk
|
||||
|
||||
Advantages:
|
||||
|
||||
* High sequential throughput
|
||||
|
||||
Disadvantages:
|
||||
|
||||
* Dedicated parity disk becomes a bottleneck.
|
||||
|
||||
Rarely used today.
|
||||
|
||||
---
|
||||
|
||||
## RAID 4
|
||||
|
||||
Uses:
|
||||
|
||||
* Block-level striping
|
||||
* One dedicated parity disk
|
||||
|
||||
Improves random reads but still suffers from the parity-disk bottleneck.
|
||||
|
||||
---
|
||||
|
||||
## RAID 5
|
||||
|
||||
**Minimum disks:** 3
|
||||
|
||||
Uses:
|
||||
|
||||
* Striping
|
||||
* Distributed parity
|
||||
|
||||
Parity blocks are spread across all drives instead of using one dedicated parity disk.
|
||||
|
||||
Advantages:
|
||||
|
||||
* Good performance
|
||||
* Efficient storage
|
||||
* Can survive one drive failure
|
||||
|
||||
Storage formula:
|
||||
|
||||
**(Number of drives − 1) × Drive size**
|
||||
|
||||
Example:
|
||||
|
||||
Four 4 TB drives → **12 TB usable**
|
||||
|
||||
Disadvantages:
|
||||
|
||||
* Slow rebuild after a failure
|
||||
* A second drive failure during rebuild causes complete data loss
|
||||
|
||||
---
|
||||
|
||||
## RAID 6
|
||||
|
||||
Similar to RAID 5 but stores **two parity blocks**.
|
||||
|
||||
Advantages:
|
||||
|
||||
* Can survive two simultaneous disk failures.
|
||||
* Better suited for very large storage arrays.
|
||||
|
||||
Disadvantages:
|
||||
|
||||
* More storage overhead
|
||||
* Slightly slower writes due to additional parity calculations
|
||||
|
||||
Storage formula:
|
||||
|
||||
**(Number of drives − 2) × Drive size**
|
||||
|
||||
---
|
||||
|
||||
## RAID 10 (1+0)
|
||||
|
||||
Combines:
|
||||
|
||||
* RAID 1 (mirroring)
|
||||
* RAID 0 (striping)
|
||||
|
||||
Requires at least four disks.
|
||||
|
||||
Advantages:
|
||||
|
||||
* Excellent performance
|
||||
* High fault tolerance
|
||||
* Fast rebuilds
|
||||
|
||||
Disadvantages:
|
||||
|
||||
* Only 50% of storage is usable
|
||||
|
||||
Widely used for:
|
||||
|
||||
* Databases
|
||||
* Virtual machines
|
||||
* Enterprise servers
|
||||
|
||||
---
|
||||
|
||||
# Nested RAID Levels
|
||||
|
||||
Some RAID systems combine multiple RAID levels, including:
|
||||
|
||||
* RAID 01
|
||||
* RAID 10
|
||||
* RAID 50
|
||||
* RAID 60
|
||||
|
||||
These combinations aim to balance speed, storage efficiency, and fault tolerance for specific workloads. ([Harvey Mudd College][1])
|
||||
|
||||
---
|
||||
|
||||
# RAID Implementations
|
||||
|
||||
### Hardware RAID
|
||||
|
||||
A dedicated RAID controller manages the array.
|
||||
|
||||
Advantages:
|
||||
|
||||
* Better performance
|
||||
* Less CPU usage
|
||||
* Often includes battery-backed cache
|
||||
|
||||
Disadvantages:
|
||||
|
||||
* More expensive
|
||||
* Hardware failures may require a compatible controller
|
||||
|
||||
---
|
||||
|
||||
### Software RAID
|
||||
|
||||
The operating system manages the RAID.
|
||||
|
||||
Advantages:
|
||||
|
||||
* No special hardware required
|
||||
* Lower cost
|
||||
* Flexible configuration
|
||||
|
||||
Disadvantages:
|
||||
|
||||
* Uses CPU resources
|
||||
* Performance depends on the operating system
|
||||
|
||||
Examples include Linux `mdadm`, Windows Storage Spaces, and ZFS/Btrfs (which provide RAID-like capabilities).
|
||||
|
||||
---
|
||||
|
||||
### Firmware ("Fake RAID")
|
||||
|
||||
Implemented in motherboard firmware with operating system drivers.
|
||||
|
||||
Advantages:
|
||||
|
||||
* Cheaper than dedicated hardware RAID
|
||||
|
||||
Disadvantages:
|
||||
|
||||
* Often offers little performance benefit over software RAID
|
||||
* May have compatibility issues
|
||||
|
||||
---
|
||||
|
||||
# Reliability and Weaknesses
|
||||
|
||||
Although RAID improves reliability, it has limitations:
|
||||
|
||||
### RAID is **not a backup**
|
||||
|
||||
RAID protects against hardware failures but does **not** protect against:
|
||||
|
||||
* Accidental deletion
|
||||
* Malware or ransomware
|
||||
* File corruption
|
||||
* Fire, flood, or theft
|
||||
* Human error
|
||||
|
||||
Regular backups are still essential.
|
||||
|
||||
---
|
||||
|
||||
### Rebuild Time
|
||||
|
||||
When a failed drive is replaced, RAID rebuilds the lost data.
|
||||
|
||||
Modern large-capacity drives (e.g., 20 TB or more) can take many hours or even days to rebuild, during which the array is more vulnerable to additional failures. ([Harvey Mudd College][1])
|
||||
|
||||
---
|
||||
|
||||
### Unrecoverable Read Errors (UREs)
|
||||
|
||||
During a rebuild, if another disk has an unreadable sector, the rebuild may fail—especially in RAID 5. This is one reason RAID 6 is often preferred for large arrays. ([Harvey Mudd College][1])
|
||||
|
||||
---
|
||||
|
||||
## Choosing the Right RAID Level
|
||||
|
||||
| RAID Level | Speed | Fault Tolerance | Storage Efficiency | Typical Use |
|
||||
| ---------- | --------: | --------------: | -----------------: | ---------------------------------- |
|
||||
| RAID 0 | Excellent | None | 100% | High-performance workloads |
|
||||
| RAID 1 | Good | High | 50% | Critical personal or business data |
|
||||
| RAID 5 | Good | One drive | High | General-purpose servers |
|
||||
| RAID 6 | Good | Two drives | Moderate | Large storage systems |
|
||||
| RAID 10 | Excellent | High | 50% | Databases and virtualization |
|
||||
|
||||
### Key Takeaways
|
||||
|
||||
* RAID combines multiple drives to improve **performance**, **availability**, and/or **fault tolerance**.
|
||||
* Different RAID levels use **striping**, **mirroring**, and **parity** in different combinations.
|
||||
* RAID 0 maximizes speed but provides no protection.
|
||||
* RAID 1 focuses on data redundancy through mirroring.
|
||||
* RAID 5 and RAID 6 use parity to balance capacity and reliability.
|
||||
* RAID 10 delivers both high performance and strong redundancy but requires more disks and sacrifices half the raw storage capacity.
|
||||
* RAID helps protect against disk failures, but it is **not a substitute for regular backups**.
|
||||
Reference in New Issue
Block a user