RAID CONCEPT

Presentation

1. RAID Concepts
Engenio Storage Group
Internal RAID
2008

2. 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

3. 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)

4. 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

5. LSI Confidential 5
RAID 0 - Striping
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.
Definition
No Fault Tolerance
Minimum 1 / Maximum 64 Drives
Non-critical data requiring high performance
Environments that do not require fault tolerance
Uses
No fault tolerance: If any drive in the array fails, all data is
lost
Drawbacks
High data throughput, especially for large files
No capacity loss penalty for parity.
Benefits

6. LSI Confidential 6
RAID 0

7. LSI Confidential 7
RAID 1: Mirroring
Mirroring - writes duplicate data to more than one (usually
two) drives
Protects against data loss in the event of a device failure
Definition
Yes Fault Tolerance
2 Drives
If availability is critical
Use RAID 1 for small databases or any other environment that
requires fault tolerance but small capacity
Uses
Expensive: Requires two drives for the storage space of
one drive
Reduced Performance during drive rebuilds.
Drawbacks
Provides 100% data redundancy
Should one drive fail, the controller switches reads and
writes to the other drive.
Benefits

8. LSI Confidential 8
RAID 1

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RAID 5 : Striping with Rotational Parity
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
Definition
Yes Fault Tolerance
Minimum 3 Drives
Any application that has high read request rates and
average write request rates
Transaction servers, web servers, data mining applications,
exchange servers
Uses
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
Drawbacks
Uses one disk worth of space to achieve data redundancy
If a hot spare is available, it can perform a rebuild
automatically
Benefits

10. LSI Confidential 10
RAID 5

11. LSI Confidential 11
RAID 10 : Spanning two RAID 1’s
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)
Definition
Yes Fault Tolerance
Minimum 4 / Maximum 16 Drives
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.
Uses
Requires half the available disk space for data redundancy
Same as RAID level 1.
Drawbacks
Optimized for both fault tolerance and performance
Provides both high data transfer rates and complete data
redundancy
Benefits

12. LSI Confidential 12
RAID 50 : Spanning two RAID 5’s
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.
Definition
Yes Fault Tolerance
Minimum 6 Drives
RAID 50 works best when used with data that requires high
reliability, high request rates, and high data transfer and
medium to large capacity.
Uses
Requires at least twice as many parity drives as a single
RAID 5.
Drawbacks
RAID 50 provides high data throughput, data redundancy,
and very good performance.
Benefits

13. LSI Confidential 13
RAID 50

14. LSI Confidential 14
RAID 0+1 Enhanced Mirroring
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.
Definition
Yes Fault Tolerance
Minimum 4 Drives
If a drive fails, the controller uses the parity drive to recreate
all missing information.
Uses
Requires half the available disk space for data redundancy,
the same as RAID level 1.
Drawbacks
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.
Benefits

15. LSI Confidential 15
RAID 0+1

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RAID 1E Enhanced Mirroring
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.
Definition
Yes Fault Tolerance
Minimum 3 Drives
When array availability is most important
For small databases or any other environment that requires
fault tolerance but small capacity
Uses
50% storage efficiency Drawbacks
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.
Benefits

17. LSI Confidential 17
RAID 1E

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JBOD: Single Drive Control
No Fault Tolerance
Works best when used if you have odd sized drives and
you want to combine them to make one big drive Uses
Decreases performance because of the difficulty in using
drives concurrently or to optimize drives for different uses Drawbacks
Single drive control - the ability to combine odd size drives
using all of the capacity of the drives. Benefits

19. LSI Confidential 19
RAID 6 : Striping with Dual Rotational Parity
Distributed parity – disk striping and two independent parity
blocks per stripe
Can survive the loss of two disks without losing data
Definition
Yes Fault Tolerance
Minimum 3 Drives
Any application that has high read request rates and
average write request rates
Transaction servers, web servers, data mining applications,
exchange servers
Uses
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
Drawbacks
Data redundancy, high read rates, and good performance Benefits

20. 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