RAID CONCEPT
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Transcript of RAID CONCEPT
RAID Concepts
Engenio Storage GroupInternal RAID
2008
LSI Confidential 2
RAID Concepts
• Objective: At the end of this presentation you will be able to …
– Discuss basic RAID technology market positioning
– Explain the inherent advantages of using RAID
– Identify appropriate RAID levels to use for specific platforms and applications
LSI Confidential 3
What is RAID?
• 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)
LSI Confidential 4
RAID Level Overview
• Selecting the proper RAID level for a specific data storage application requires consideration be given to the benefits of each
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
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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.
BenefitsHigh data throughput, especially for large filesNo 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
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RAID 0
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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
LSI Confidential 8
RAID 1
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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
LSI Confidential 10
RAID 5
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RAID 10 : Spanning two RAID 1’s
DefinitionSpanning 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
LSI Confidential 12
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.
UsesRAID 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
LSI Confidential 13
RAID 50
LSI Confidential 14
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.
BenefitsOptimizes 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
LSI Confidential 15
RAID 0+1
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RAID 1E Enhanced Mirroring
Definition
Enhanced mirroring - combines mirroring with data striping The first set of stripes are the data, and the second set of
stripes are mirrors of the first data stripe contained within the next logical drive.
Benefits
Shares the characteristics of RAID 1, but allows more than two drives, including odd numbers of drives
If one of the drives fails, the controller switches read and write requests to the remaining functional drives in the RAID level-1E array.
Drawbacks 50% storage efficiency
Uses When array availability is most important For small databases or any other environment that requires
fault tolerance but small capacity
Drives Minimum 3
Fault Tolerance Yes
LSI Confidential 17
RAID 1E
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JBOD: Single Drive Control
BenefitsSingle drive control - the ability to combine odd size drives using all of the capacity of the drives.
Drawbacks Decreases performance because of the difficulty in using
drives concurrently or to optimize drives for different uses
Uses Works best when used if you have odd sized drives and
you want to combine them to make one big drive
Fault Tolerance No
LSI Confidential 19
RAID 6 : Striping with Dual Rotational Parity
DefinitionDistributed parity – disk striping and two independent parity
blocks per stripe Can survive the loss of two disks without losing data
Benefits Data redundancy, high read rates, and good performance
Drawbacks
Requires two sets of parity data for each write operation, resulting in significant decrease in write performance
Additional costs because of the extra capacity required by using two parity blocks per stripe
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
LSI Confidential 20
RAID 6
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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