Latest Developments In Raid Technology Biology Essay

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RAID (redundant array of independent disks, originally redundant array of inexpensive disks) is a way of storing the same data in different places (thus, redundantly) on multiple hard disks.

As we have already discussed the different types of RAID in the class. I will be discussing the developments in RAID technology after RAID 6.

RAID Level 7:

Unlike the other RAID levels, RAID 7 isn't an open industry standard; it is really a trademarked marketing term of Storage Computer Corporation, used to describe their proprietary RAID design. (I debated giving it a page alongside the other RAID levels, but since it is used in the market, it deserves to be explained; that said, information about it appears to be limited.) RAID 7 is based on concepts used in RAID levels 3 and 4, but greatly enhanced to address some of the limitations of those levels. Of particular note is the inclusion of a great deal of cache arranged into multiple levels, and a specialized real-time processor for managing the array asynchronously. This hardware support--especially the cache--allow the array to handle many simultaneous operations, greatly improving performance of all sorts while maintaining fault tolerance. In particular, RAID 7 offers much improved random read and write performance over RAID 3 or RAID 4 because the dependence on the dedicated parity disk is greatly reduced through the added hardware. The increased performance of RAID 7 of course comes at a cost. This is an expensive solution, made and supported by only one company.

Some Facts related to RAID 7:-

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Controller Requirements: Requires a specialized, expensive, proprietary controller.

Hard Disk Requirements: Depends on implementation.

Array Capacity: Depends on implementation.

Storage Efficiency: Depends on implementation.

Fault Tolerance: Very good.

Availability: Excellent, due to use of multiple hot spares.

Degradation and Rebuilding: Better than many RAID levels due to hardware support for parity calculation operations and multiple cache levels.

Random Read Performance: Very good to excellent. The extra cache can often supply the results of the read without needing to access the array drives.

Random Write Performance: Very good; substantially better than other single RAID levels doing striping with parity.

Sequential Read Performance: Very good to excellent.

Sequential Write Performance: Very good.

Cost: Very high.

RAID Levels (01)

Technique(s) Used: Mirroring and striping without parity.

Description: The most popular of the multiple RAID levels, RAID 01 and 10 combine the best features of striping and mirroring to yield large arrays with high performance in most uses and superior fault tolerance. RAID 01 is a mirrored configuration of two striped sets; RAID 10 is a stripe across a number of mirrored sets. RAID 10 and 01 have been increasing dramatically in popularity as hard disks become cheaper and the four-drive minimum is legitimately seen as much less of an obstacle. RAID 10 provides better fault tolerance and rebuild performance than RAID 01. Both array types provide very good to excellent overall performance by combining the speed of RAID 0 with the redundancy of RAID 1 without requiring parity calculations.

Some Facts related to RAID 01:-

Controller Requirements: Almost all hardware controllers will support one or the other of RAID 10 or RAID 01, but often not both. Even low-end cards will support this multiple level, usually RAID 01. High-end cards may support both 01 and 10.

Hard Disk Requirements: An even number of hard disks with a minimum of four; maximum dependent on controller. All drives should be identical.

Array Capacity: (Size of Smallest Drive) * (Number of Drives ) / 2.

Storage Efficiency: If all drives are the same size, 50%.

Fault Tolerance: Very good for RAID 01; excellent for RAID 10.

Availability: Very good for RAID 01; excellent for RAID 10.

Degradation and Rebuilding: Relatively little for RAID 10; can be more substantial for RAID 01.

Random Read Performance: Very good to excellent.

Random Write Performance: Good to very good.

Sequential Read Performance: Very good to excellent.

Sequential Write Performance: Good to very good.

Cost: Relatively high due to large number of drives required and low storage efficiency (50%).

Special Considerations: Low storage efficiency limits potential array capacity.

RAID-50

Common Name(s): RAID 0+5 or 05; RAID 5+0 or 50. As with the other multiple RAID levels, verify the exact implementation instead of relying on the label.

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Technique(s) Used: Block striping with distributed parity combined with block striping.

Description: RAID 05 and 50 form large arrays by combining the block striping and parity of RAID 5 with the straight block striping of RAID 0. RAID 05 is a RAID 5 array comprised of a number of striped RAID 0 arrays; it is less commonly seen than RAID 50, which is a RAID 0 array striped across RAID 5 elements. RAID 50 and 05 improve upon the performance of RAID 5 through the addition of RAID 0, particularly during writes. It also provides better fault tolerance than the single RAID level does, especially if configured as RAID 50.

Some Facts related to RAID 50:-

Controller Requirements: Generally requires a high-end hardware controller.

Hard Disk Requirements: Number of drives must be able to be factored into two integers, one of which must be 2 or higher and the other 3 or higher (you can make a RAID 30 array from 6 drives but not 7). Minimum number of drives is six, with the maximum set by the controller.

Storage Efficiency: Same as for RAID 03 and 30. For RAID 05: ( (Number of RAID 0 Sets - 1) / Number of RAID 0 Sets). For RAID 50: ( (Number of Drives In Each RAID 5 Set - 1) / Number of Drives In Each RAID 5 Set).

Fault Tolerance: Same as for RAID 03 and 30. Good to very good, depending on whether it is RAID 05 or 50, and the number of parity drives relative to the total number. RAID 50 will provide better fault tolerance than RAID 05.

Consider the two different 21-drive RAID 50 arrays mentioned above: the first one (three seven-drive RAID 5 sets) has higher capacity and storage efficiency, but can only tolerate three maximum potential drive failures; the one with lower capacity and storage efficiency (seven three-drive RAID 5 sets) can handle as many as seven , if they are in different RAID 5 sets. Of course few applications really require tolerance for seven independent drive failures! And of course, if those 21 drives were in a RAID 05 array instead, failure of a second drive after one had failed and taken down one of the RAID 0 sub-arrays would crash the entire array.

Availability: Very good to excellent.

Degradation and Rebuilding: Moderate for RAID 50; worse for RAID 05.

Random Read Performance: Very good to excellent.

Random Write Performance: Good.

Sequential Read Performance: Very good.

Sequential Write Performance: Good.

Cost: Relatively high due to requirements for a hardware controller and a large number of drives; storage efficiency is better than RAID 10 however and no worse than any other RAID levels that include redundancy.

Special Considerations: Complex and expensive to implement.

Recommended Uses: Applications that require high fault tolerance, capacity and random positioning performance. Not as widely used as many other RAID levels. Sometimes used instead of RAID 5 to increase capacity. Sometimes used for large databases.

RAID-53:

Description: RAID 03 and 30 (though often called 53 for a reason that utterly escapes me) combine byte striping, parity and block striping to create large arrays that are conceptually difficult to understand. :^) RAID 03 is formed by putting into a RAID 3 array a number of striped RAID 0 arrays; RAID 30 is more common and is formed by striping across a number of RAID 3 sub-arrays. The combination of parity, small-block striping and large-block striping makes analyzing the theoretical performance of this level difficult. In general, it provides performance better than RAID 3 due to the addition of RAID 0 striping, but closer to RAID 3 than RAID 0 in overall speed, especially on writes. RAID 30 provides better fault tolerance and rebuild performance than RAID 03, but both depend on the "width" of the RAID 3 dimension of the drive relative to the RAID 0 dimension: the more parity drives, the lower capacity and storage efficiency, but the greater the fault tolerance. See the examples below for more explanation of this.

Most of the characteristics of RAID 0+3 and 3+0 are similar to those of RAID 0+5 and 5+0. RAID 30 and 03 tend to be better for large files than RAID 50 and 05.

Controller Requirements: Generally requires a high-end hardware controller.

Hard Disk Requirements: Number of drives must be able to be factored into two integers, one of which must be 2 or higher and the other 3 or higher (you can make a RAID 30 array from 10 drives but not 11). Minimum number of drives is six, with the maximum set by the controller.

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Storage Efficiency: For RAID 03: ( (Number of RAID 0 Sets - 1) / Number of RAID 0 Sets). For RAID 30: ( (Number of Drives In Each RAID 3 Set - 1) / Number of Drives In Each RAID 3 Set).

Taking the same examples as above, the 15-drive RAID 03 array would have a storage efficiency of (3-1)/3 = 67%. The first RAID 30 array, configured as three seven-drive RAID 3 sets, would have a storage efficiency of (7-1)/7 = 86%, while the other RAID 30 array would have a storage efficiency of, again, (3-1)/3 = 67%.

Fault Tolerance: Good to very good, depending on whether it is RAID 03 or 30, and the number of parity drives relative to the total number. RAID 30 will provide better fault tolerance than RAID 03.

Consider the two different 21-drive RAID 30 arrays mentioned above: the first one (three seven-drive RAID 3 sets) has higher capacity and storage efficiency, but can only tolerate three maximum potential drive failures; the one with lower capacity and storage efficiency (seven three-drive RAID 3 sets) can handle as many as seven , if they are in different RAID 3 sets. Of course few applications really require tolerance for seven independent drive failures! And of course, if those 21 drives were in a RAID 03 array instead, failure of a second drive after one had failed and taken down one of the RAID 0 sub-arrays would crash the entire array.

Availability: Very good to excellent.

Degradation and Rebuilding: Relatively little for RAID 30 (though more than RAID 10); can be more substantial for RAID 03.

Random Read Performance: Very good, assuming RAID 0 stripe size is reasonably large.

Random Write Performance: Fair.

Sequential Read Performance: Very good to excellent.

Sequential Write Performance: Good.

Cost: Relatively high due to requirements for a hardware controller and a large number of drives; storage efficiency is better than RAID 10 however and no worse than any other RAID levels that include redundancy.

Special Considerations: Complex and expensive to implement.

Refrences:

Book: A Source Book for Raid Technology

Internet source Author: Charles M. Kozierok.

http://www.pcguide.com/ref/hdd/perf/raid/levels/