What are different levels of RAID RAID 0 1 5 6 and 10?

RAID (Redundant Array of Independent Disks) is a data storage technology that combines multiple disk drive components into a logical unit. Data is distributed across the drives in one of several ways called RAID levels, depending on the level of redundancy and performance required. The different levels of RAID provide different blends of these key features:

What are the benefits of using RAID?

There are several key benefits to using RAID technology:

  • Increased data reliability and fault tolerance – RAID provides protection against drive failures by duplicating data across multiple drives. If one drive fails, data can still be accessed from the remaining drives.
  • Improved performance – In some RAID levels, input/output (I/O) operations can be distributed across multiple drives for faster data access.
  • Greater storage capacity – Multiple disk drives can be combined into a larger logical volume, allowing for more storage capacity.

By leveraging an array of disks, RAID aims to provide increased storage reliability, better performance, or both. The specific advantages depend on the RAID level used.

What are the different levels of RAID?

There are several standard RAID levels, each with their own benefits, drawbacks and use cases:

RAID 0

  • Description – RAID 0 stripes data across multiple drives with no redundancy. All storage capacity is used.
  • Benefits – Very fast read/write speeds. High utilization of disk capacity.
  • Drawbacks – No fault tolerance. Loss of one drive causes total data loss.
  • Use cases – Temporary storage, scratch disks, video editing.

RAID 1

  • Description – RAID 1 mirrors data between two disks. Provides 100% redundancy.
  • Benefits – Very high read performance. Complete data protection with drive mirroring.
  • Drawbacks – 50% storage overhead since data is duplicated. Slow writes.
  • Use cases – Critical systems requiring maximum resilience.

RAID 5

  • Description – RAID 5 stripes data and parity information across 3+ disks. Can withstand one disk failure.
  • Benefits – Good read performance. Cost efficient redundant storage.
  • Drawbacks – Slow writes. Rebuilding array is slow after drive failure.
  • Use cases – File and application servers, databases.

RAID 6

  • Description – RAID 6 extends RAID 5 by adding a second parity block. Can withstand two disk failures.
  • Benefits – Excellent fault tolerance and protection against data loss.
  • Drawbacks – Higher capacity overhead for dual parity than RAID 5.
  • Use cases – Mission critical storage that requires high resilience.

RAID 10

  • Description – RAID 10 mirrors two drives, then stripes these sets in a RAID 0 config.
  • Benefits – Very high performance, especially for read operations. Fault tolerance.
  • Drawbacks – 50% capacity overhead just like RAID 1 mirroring.
  • Use cases – High performance databases, virtualization, and transactional systems.

Key characteristics of common RAID levels

Here is a summary of key characteristics for the most common RAID levels:

RAID Level Minimum Drives Capacity Efficiency Fault Tolerance Read Performance Write Performance
RAID 0 2 100% None Excellent Excellent
RAID 1 2 50% Excellent Excellent Poor
RAID 5 3 67% – 94% Good Good Poor
RAID 6 4 50% – 88% Excellent Good Poor
RAID 10 4 50% Excellent Excellent Good

As seen in the table, different RAID levels involve trade-offs between performance, capacity efficiency, and fault tolerance. When selecting a RAID level, it is important to match the characteristics of the RAID solution with your application requirements and availability needs.

Choosing the right RAID level

There are several factors to consider when choosing the appropriate RAID level:

  • Application performance needs – Does the application require faster reads or writes? RAID 0 provides overall fast performance while RAID 1 optimizes reads.
  • Capacity requirements – RAID 5, 6 provide efficient use of storage, while RAID 1 and 10 have significant overhead.
  • Availability and redundancy needs – RAID 1, 5, 6, and 10 provide fault tolerance. RAID 6 offers maximum protection.
  • Rebuild times – RAID levels with parity (5, 6) have long rebuild times. RAID 1 and 10 rebuild faster.
  • Budget – Solutions range from low-cost software RAID to expensive hardware RAID cards.

In summary:

  • RAID 0 maximizes speed and capacity utilization but offers no redundancy.
  • RAID 1 provides guaranteed mirroring and fast rebuilds but uses 50% overhead.
  • RAID 5 offers single-disk fault tolerance and good read performance for a low cost.
  • RAID 6 extends RAID 5 for environments needing high availability and uptime.
  • RAID 10 combines mirroring and striping for fast performance but also incurs 50% overhead.

Hardware vs. software RAID

RAID can be implemented in two ways:

  • Hardware RAID – Uses a dedicated RAID controller card with on-board cache and processing.
  • Software RAID – Managed by the operating system using the system’s CPU and memory resources.

Hardware RAID advantages:

  • Higher and more consistent performance, especially for writes.
  • Unburdens host system resources.
  • Possible to do RAID recovery and rebuilding without a host system.
  • More maturity and advanced feature sets.

Software RAID advantages:

  • Lower cost to implement – uses existing system hardware.
  • Easier to manage RAID through software interface.
  • Added flexibility in some cases.

Hardware RAID is preferred for mission critical systems that demand peak performance. Software RAID provides a lower cost option where hardware cost is a concern and performance needs are moderate.

Implementation best practices

Here are some best practices to follow when implementing RAID:

  • Select RAID levels based on performance, capacity, and availability needs.
  • Use higher performing RAID levels for applications with heavy write workloads like databases.
  • Ensure RAID cards or motherboards support the desired RAID level.
  • Use enterprise class SAS or SSD drives which are made for RAID vs cheaper SATA drives.
  • Use at least 10K RPM drives for RAID configurations focused on performance.
  • Ensure RAID card has batteries or flash storage for write-back cache protection.
  • Monitor disk health and utilization to identify problems early.
  • Have hot spare drives ready to rebuild arrays quickly after a failure.
  • Test recovery procedures regularly to validate they work when needed.

Conclusion

RAID allows combining multiple storage drives to achieve increased capacity, speed, availability or a combination. Key considerations for implementation include performance needs, fault tolerance level, and cost. RAID improves storage performance and resilience through parallelism and redundancy. Matching the strengths of specific RAID levels with application requirements is key to maximizing benefits.