Lesson 8	RAID basics
Objective	Explain basic concepts related to RAID

Basic Concepts of RAID in Red Hat Linux

"RAID" (Redundant Array of Independent/Inexpensive Disks) is a technology that combines multiple physical disks into a single logical unit to achieve data redundancy, improved performance, or both. RAID is widely used in Linux systems, including Red Hat Linux, to enhance data reliability and storage efficiency.
Here are the key concepts related to RAID:

RAID Levels
- RAID 0 (Striping)
  - Data is split across multiple disks for improved performance.
  - No redundancy; if one disk fails, all data is lost.
  - Best for performance-focused applications like video editing.
- RAID 1 (Mirroring)
  - Data is duplicated (mirrored) across two or more disks.
  - High redundancy; data remains accessible if one disk fails.
  - Suitable for critical systems requiring data reliability.
- RAID 5 (Striping with Parity)
  - Combines striping and parity information across three or more disks.
  - Allows recovery from a single disk failure.
  - Balanced performance and redundancy; widely used in servers.
- RAID 6 (Striping with Double Parity)
  - Similar to RAID 5 but with two parity blocks, allowing recovery from up to two disk failures.
  - Requires a minimum of four disks.
- RAID 10 (1+0, Mirroring + Striping)
  - Combines RAID 1 (mirroring) and RAID 0 (striping).
  - Provides high performance and redundancy but requires at least four disks.
RAID Types in Red Hat Linux
- Software RAID
  - Managed by the operating system using tools like mdadm.
  - Cost-effective as it doesn't require special hardware.
  - Fully supported in Red Hat Linux and can be configured during or after installation.
- Hardware RAID
  - Managed by a dedicated RAID controller.
  - Reduces CPU usage but may be more expensive.
  - Requires RAID drivers compatible with Red Hat Linux.
Key RAID Concepts
- Striping
  - Data is split into blocks and written across multiple disks.
  - Improves read/write performance but lacks redundancy (RAID 0).
- Mirroring
  - Entire copies of data are stored on multiple disks.
  - Provides redundancy and fault tolerance (RAID 1).
- Parity
  - Uses additional information to rebuild data in case of disk failure.
  - Efficient use of disk space while providing redundancy (RAID 5/6).
- Hot Spare
  - A spare disk is included in the RAID array and automatically replaces a failed disk.
  - Ensures continuous redundancy without manual intervention.
RAID Benefits
- Data Redundancy
  - Protects against disk failures and ensures data availability.
- Improved Performance
  - RAID levels like 0, 5, and 10 enhance read/write speeds, benefiting resource-intensive applications.
- Cost Efficiency
  - Uses inexpensive disks to create high-performance, fault-tolerant storage.
- Scalability
  - RAID arrays can be expanded by adding more disks (depending on RAID level).
RAID in Red Hat Linux
- Installation and Management
  - RAID can be set up during installation using Red Hat's installer (Anaconda).
  - Post-installation, RAID arrays can be configured and managed with tools like mdadm (Multiple Device Administration).
- Monitoring and Maintenance
  - RAID arrays can be monitored using commands like cat /proc/mdstat and utilities like smartctl for disk health checks.
- Integration with LVM
  - Logical Volume Manager (LVM) can be layered over RAID to provide greater flexibility in managing storage.
RAID Limitations
- Cost
  - Higher RAID levels (e.g., RAID 10) require more disks, increasing costs.
- Complexity
  - Configuration and management of RAID arrays can be complex.
- Performance Overhead
  - RAID levels with parity (e.g., RAID 5/6) may experience write performance penalties due to parity calculations.

Conclusion RAID is a powerful tool in Red Hat Linux for achieving a balance of performance, redundancy, and cost-efficiency. With tools like `mdadm` and support for hardware RAID controllers, RHEL provides robust options for configuring and managing RAID arrays to meet the needs of enterprise environments.

RAID (Redundant Array of Inexpensive Disks) is a valuable tool that combines data redundancy with improved performance and reduced cost. It enables you to write to several distinct disks as one drive. This decreases costs for an organization by allowing many inexpensive drives to act as one large logical drive. Depending on the needs of an organization, an appropriate RAID level can be chosen to support duplication of data, increased access speed, or minimized expense. RAID's advantages include:

Combining multiple disks to create a single logical disk
Minimizing the effect of a single drive failure
Increasing performance in some instances

The next lesson describes RAID levels.

Creating RAID Arrays

In addition to supporting hardware RAID solutions, Red Hat Enterprise Linux supports software RAID. There are two ways that software RAID arrays can be created:

While installing Red Hat Enterprise Linux
After Red Hat Enterprise Linux has been installed

The following sections review these two methods.

While Installing Red Hat Enterprise Linux During the normal Red Hat Enterprise Linux installation process, RAID arrays can be created. This is done during the disk partitioning phase of the installation.
To begin, you must manually partition your disk drives using Disk Druid. You must first create a new partition of the type "software RAID." Next, select the disk drives that you want to be part of the RAID array in the Allowable Drives field. Continue by selecting the desired size and whether you want the partition to be a primary partition.
Once you have created all the partitions required for the RAID array(s) that you want to create, you must then use the RAID button to actually create the arrays. You are then presented with a dialog box where you can select the array's mount point, file system type, RAID device name, RAID level, and the "software RAID" partitions on which this array is to be based.
Once the desired arrays have been created, the installation process continues as usual.