RAID (Redundant Array of Independent Disks) is a data storage technology that combines multiple disk drive components into a logical unit. RAID offers fault tolerance and improves performance over a single disk.
There are several different RAID modes, each with their own benefits and drawbacks. Understanding the key differences between RAID modes can help you choose the right configuration for your needs.
The Core Benefits of RAID
There are two core benefits provided by RAID:
Redundancy – RAID allows data to be duplicated across multiple drives, so if one disk fails, the data can still be accessed from another disk. This prevents data loss and downtime.
I should note that RAID should not be considered a replacement for backing up your data. If critical data is going onto a RAID array, it should be backed up to another physical drive or logical set of drives.
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Performance – RAID can spread data across multiple disks in a way that allows increased read/write speeds. This is useful for applications that require high throughput. Multiple disk heads can read/write data in parallel.
Common RAID Modes and Levels
There are several standard RAID modes, referred to by different RAID levels. Each RAID level has its own balance of performance, redundancy, and storage efficiency:
The following are terms that are normally used in connection with RAID:
- Striping: data is split between multiple disks.
- Mirroring: data is mirrored between multiple disks.
- Parity: also referred to as a checksum. Parity is a calculated value used to mathematically rebuild data.
RAID 0 – Striping without parity. RAID 0 splits and duplicates data across multiple disks for improved performance, but does not provide redundancy. If one drive fails, all data will be lost.
RAID 1 – Mirroring without parity. RAID 1 duplicates all data across two disks to provide full redundancy, but does not improve performance over a single disk.
RAID 5 – Striping with distributed parity. RAID 5 stripes data across multiple disks like RAID 0, but also dedicates one disk’s capacity for parity data that can reconstruct data if a disk fails. RAID 5 provides both improved performance and redundancy.
RAID 6 – Striping with multiple distributed parity disks. RAID 6 is similar to RAID 5 but dedicates the capacity of two disks to parity data instead of one. This allows data reconstruction if up to two disks fail.
RAID 10 – Mirroring and striping. RAID 10 mirrors two strips of disks, providing the redundancy of RAID 1 plus the performance of RAID 0. However, 50% of the total capacity is needed for redundancy alone.
Choosing the Right RAID Level
When choosing a RAID level, key factors to consider include:
- Storage capacity needed
- Redundancy required
- Performance requirements
- Number of disks available
For example, RAID 0 provides the best performance but no redundancy. RAID 1 provides full redundancy with no capacity or performance gain. RAID 5 is a good balance for both redundancy and performance with reasonable storage efficiency. RAID 6 offers high redundancy for critical data but at the cost of more disk capacity dedicated to parity.
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RAID 10 combines mirroring and stripping for both high performance and redundancy but at the cost of high disk capacity requirements. Considering the specific storage, performance and redundancy needs of your application is important when selecting a RAID mode.
Implementing RAID
RAID can be implemented in a few different ways:
- Hardware RAID uses a dedicated RAID controller to manage the RAID disks. This simplifies configuration but can be less flexible.
- Software RAID is implemented at the operating system level, so no special hardware is needed. This provides more flexibility but puts a slight load on the CPU.
- Fake/containerized RAID uses abstraction and mapping to emulate RAID without dedicated hardware or software. This approach provides RAID-like redundancy without true hardware RAID.
RAID improves performance and protects against data loss but does not replace a true backup solution. Regular backups to external systems are still recommended even when using RAID to fully protect important data.
As storage needs evolve, understanding the core RAID concepts can help select the right RAID configuration for optimal performance, redundancy and capacity.
