- RAID stands for an redundant array of independent drives
- Intelligently manages drives in unison performing data read/write algorithms across drives delivering
–High levels of protection against downtime and data loss (mirroring)
–Larger storage volumes achievable
–Improved performance (striping)
RAID Level Overview
- Selecting the proper RAID level for a specific data storage application requires consideration be given to the benefits of each
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LSI Supported • RAID 0 (1 to 32 disks) • RAID 1 (2 disks) • RAID 5 (3 to 32 disks) • RAID 10 (4 to 16 disks) • RAID 50 (6 to 60 disks) • RAID 6 |
Use • Video/Audio streaming • OS boot • Transaction/Web server • Database • Data warehousing • Large capacity disk arrays |
RAID 0 – Striping
| Definition |
Striping – writes data across multiple drives §Involves partitioning each drive storage space into stripes that can vary in size from 2 KB to 1 MB. §These stripes are interleaved in a repeated sequential manner. |
| Benefits |
§High data throughput, especially for large files §No capacity loss penalty for parity. |
| Drawbacks | §No fault tolerance: If any drive in the array fails, all data is lost |
| Uses |
§Non-critical data requiring high performance §Environments that do not require fault tolerance |
| Drives | Minimum 1 / Maximum 64 |
| Fault Tolerance | No |
RAID 1: Mirroring
| Definition |
Mirroring – writes duplicate data to more than one (usually two) drives §Protects against data loss in the event of a device failure |
| Benefits |
§Provides 100% data redundancy §Should one drive fail, the controller switches reads and writes to the other drive. |
| Drawbacks |
§Expensive: Requires two drives for the storage space of one drive §Reduced Performance during drive rebuilds. |
| Uses |
§If availability is critical §Use RAID 1 for small databases or any other environment that requires fault tolerance but small capacity |
| Drives | 2 |
| Fault Tolerance | Yes |
RAID 5 : Striping with Rotational Parity
| Definition |
Striping with rotational parity – blocks of data and parity information is stripped across all drives §RAID level 5 is the most popular configuration, providing striping as well as parity for error recovery |
| Benefits |
§Uses one disk worth of space to achieve data redundancy §If a hot spare is available, it can perform a rebuild automatically |
| Drawbacks |
§Cannot match RAID 0 in write performance due to processing required to compute parity §While a controller is rebuilding a drive, users will experience reduced performance if reading or writing data |
| Uses |
§Any application that has high read request rates and average write request rates §Transaction servers, web servers, data mining applications, exchange servers |
| Drives | Minimum 3 |
| Fault Tolerance | Yes |
RAID 10 : Spanning two RAID 1’s
| Definition | Spanning two RAID 1’s – writing duplicate data to more than one pair of drives to protect against data loss in the event of a up to two disk failures (one per array) |
| Benefits |
§Optimized for both fault tolerance and performance §Provides both high data transfer rates and complete data redundancy |
| Drawbacks |
§Requires half the available disk space for data redundancy §Same as RAID level 1. |
| Uses |
§Environments that require 100% redundancy of mirroring (RAID 1) and the enhanced I/O performance of stripping (RAID 0) §Ideal for smaller organizations needing a high degree of fault tolerance and moderate to medium capacity. |
| Drives | Minimum 4 / Maximum 16 |
| Fault Tolerance | Yes |
RAID 50 : Spanning two RAID 5’s
| Definition | Data is “striped” across multiple drive groups (super drive group). For data redundancy, drives are encoded with rotated XOR redundancy. RAID 50 provides the features of both RAID 0 and RAID 5. RAID 50 includes both parity and disk striping across multiple drives. |
| Benefits | RAID 50 provides high data throughput, data redundancy, and very good performance. |
| Drawbacks | Requires at least twice as many parity drives as a single RAID 5. |
| Uses | RAID 50 works best when used with data that requires high reliability, high request rates, and high data transfer and medium to large capacity. |
| Drives | Minimum 6 |
| Fault Tolerance | Yes |
RAID 0+1 Enhanced Mirroring
| Definition | The controller combines the performance of data striping (RAID 0) and the fault tolerance of disk mirroring (RAID 1). Data is striped across multiple drives and duplicated on another set of drives. |
| Benefits | Optimizes for both fault tolerance and performance. Provides excellent performance for all data needs. May be simultaneously used with other RAID levels in an array. |
| Drawbacks | Requires half the available disk space for data redundancy, the same as RAID level 1. |
| Uses | If a drive fails, the controller uses the parity drive to recreate all missing information. |
| Drives | Minimum 4 |
| Fault Tolerance | Yes |
RAID Level Summary
- RAID 0: Fastest and most efficient level but offers no fault tolerance
- RAID 1: Performance-critical, fault tolerant environments, but requires 2X storage
- RAID 5: Best choice for multi-user environments which are not write performance sensitive
- RAID 10: Ideal for environments that require 100% redundancy with enhanced I/O performance of stripping and can afford such an investment
- RAID 50: Works best when used with data that requires high reliability, high request rates, and high data transfer rates
- RAID 0+1: Optimal for applications needing both fault tolerance and performance. Provides excellent but additional capacity investment
- RAID 1E: Great choice for small databases or any other environment that need fault tolerance but have small capacity requirements
- RAID 6: Ideal for organizations of all sizes requiring data redundancy, high read rates, and good performance
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