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[ The PC Guide | Systems and Components Reference Guide | Hard Disk Drives | Hard Disk Performance, Quality and Reliability | Redundant Arrays of Inexpensive Disks (RAID) | RAID Levels | Single RAID Levels ]

RAID Level 7

Common Name(s): RAID 7.

Technique(s) Used: Asynchronous, cached striping with dedicated parity.

Description: 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.

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.

Special Considerations: RAID 7 is a proprietary product of a single company; if it is of interest then you should contact Storage Computer Corporation for more details on the specifics of implementing it. All the caching creates potential vulnerabilities in the event of power failure, making the use of one or more UPS units mandatory.

Recommended Uses: Specialized high-end applications requiring absolutely top performance and willing to live with the limitations of a proprietary, expensive solution. For most users, a multiple RAID level solution like RAID 1+0 will probably yield comparable performance improvements over single RAID levels, at lower cost.

Next: Multiple (Nested) RAID Levels

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