نمایش نتایج: از شماره 1 تا 3 از مجموع 3
سپاس ها 21سپاس
  • 6 توسط Beginner
  • 13 توسط hraeissi
  • 2 توسط hraeissi

موضوع: مقاله ای در مورد انواع RAID

  
  1. #1
    نام حقيقي: Beginner

    عضو عادی
    تاریخ عضویت
    Nov 2009
    محل سکونت
    Tehran
    نوشته
    32
    سپاسگزاری شده
    8
    سپاسگزاری کرده
    7

    مقاله ای در مورد انواع RAID



    This article is dedicated to learning almost all Types of RAIDs.


    ________________________RAID0_____________________ _________

    RAID 0
    Common Name(s): RAID 0. (Note that the term "RAID 0" is sometimes used to mean not only the conventional striping technique described here but also other "non-redundant" ways of setting up disk arrays. Sometimes it is (probably incorrectly) used just to describe a collection of disks that doesn't use redundancy.)
    Technique(s) Used: Striping (without parity)
    Description: The simplest RAID level, RAID 0 should really be called "AID", since it involves no redundancy. Files are broken into stripes of a size dictated by the user-defined stripe size of the array, and stripes are sent to each disk in the array. Giving up redundancy allows this RAID level the best overall performance characteristics of the single RAID levels, especially for its cost. For this reason, it is becoming increasingly popular by performance-seekers, especially in the lower end of the marketplace.

    Controller Requirements: Supported by all hardware controllers, both SCSI and IDE/ATA, and also most software RAID solutions.
    Hard Disk Requirements: Minimum of two hard disks (some may support one drive, the point of which escapes me); maximum set by controller. Any type may be used, but they should be of identical type and size for best performance and to eliminate "waste".
    Array Capacity: (Size of Smallest Drive * Number of Drives).
    Storage Efficiency: 100% if identical drives are used.
    Fault Tolerance: None. Failure of any drive results in loss of all data, short of specialized data recovery.
    Availability: Lowest of any RAID level. Lack of fault tolerance means no rapid recovery from failures. Failure of any drive results in array being lost and immediate downtime until array can be rebuilt and data restored from backup.
    Degradation and Rebuilding: Not applicable.
    Random Read Performance: Very good; better if using larger stripe sizes if the controller supports independent reads to different disks in the array.
    Random Write Performance: Very good; again, best if using a larger stripe size and a controller supporting independent writes.
    Sequential Read Performance: Very good to excellent.
    Sequential Write Performance: Very good.
    Cost: Lowest of all RAID levels.
    Special Considerations: Using a RAID 0 array without backing up any changes made to its data at least daily is a loud statement that that data is not important to you.
    Recommended Uses: Non-critical data (or data that changes infrequently and is backed up regularly) requiring high speed, particularly write speed, and low cost of implementation. Audio and video streaming and editing; web servers; graphic design; high-end gaming or hobbyist systems; temporary or "scratch" disks on larger machines.
    _________________________________RAID1____________ ________________________
    RAID Level 1
    Common Name(s): RAID 1; RAID 1 with Duplexing.
    Technique(s) Used: Mirroring or Duplexing
    Description: RAID 1 is usually implemented as mirroring; a drive has its data duplicated on two different drives using either a hardware RAID controller or software (generally via the operating system). If either drive fails, the other continues to function as a single drive until the failed drive is replaced. Conceptually simple, RAID 1 is popular for those who require fault tolerance and don't need top-notch read performance. A variant of RAID 1 is duplexing, which duplicates the controller card as well as the drive, providing tolerance against failures of either a drive or a controller. It is much less commonly seen than straight mirroring.

    Controller Requirements: Supported by all hardware controllers, both SCSI and IDE/ATA, and also most software RAID solutions.
    Hard Disk Requirements: Exactly two hard disks. Any type may be used but they should ideally be identical.
    Array Capacity: Size of Smaller Drive.
    Storage Efficiency: 50% if drives of the same size are used, otherwise (Size of Smaller Drive / (Size of Smaller Drive + Size of Larger Drive) )
    Fault Tolerance: Very good; duplexing even better.
    Availability: Very good. Most RAID controllers, even low-end ones, will support hot sparing and automatic rebuilding of RAID 1 arrays.
    Degradation and Rebuilding: Slight degradation of read performance; write performance will actually improve. Rebuilding is relatively fast.
    Random Read Performance: Good. Better than a single drive but worse than many other RAID levels.
    Random Write Performance: Good. Worse than a single drive, but better than many other RAID levels. )
    Sequential Read Performance: Fair; about the same as a single drive.
    Sequential Write Performance: Good; again, better than many other RAID levels.
    Cost: Relatively high due to redundant drives; lowest storage efficiency of the single RAID levels. Duplexing is still more expensive due to redundant controllers. On the other hand, no expensive controller is required, and large consumer-grade drives are rather inexpensive these days, making RAID 1 a viable choice for an individual system.
    Special Considerations: RAID 1 arrays are limited to the size of the drives used in the array. Multiple RAID 1 arrays can be set up if additional storage is required, but RAID 1+0 begins to look more attractive in that circumstance. Performance may be reduced if implemented using software instead of a hardware controller; duplexing may require software RAID and thus may show lower performance than mirroring.
    Recommended Uses: Applications requiring high fault tolerance at a low cost, without heavy emphasis on large amounts of storage capacity or top performance. Especially useful in situations where the perception is that having a duplicated set of data is more secure than using parity. For this reason, RAID 1 is popular for accounting and other financial data. It is also commonly used for small database systems, enterprise servers, and for individual users requiring fault tolerance with a minimum of hassle and cost (since redundancy using parity generally requires more expensive hardware.)

    _________________________________RAID2____________ _____________________
    RAID Level 2
    Common Name(s): RAID 2.
    Technique(s) Used: Bit-level striping with Hamming code ECC.
    Description: Level 2 is the "black sheep" of the RAID family, because it is the only RAID level that does not use one or more of the "standard" techniques of mirroring, striping and/or parity. RAID 2 uses something similar to striping with parity, but not the same as what is used by RAID levels 3 to 7. It is implemented by splitting data at the bit level and spreading it over a number of data disks and a number of redundancy disks. The redundant bits are calculated using Hamming codes, a form of error correcting code (ECC). Each time something is to be written to the array these codes are calculated and written oalng side the data to dedicated ECC disks; when the data is read back these ECC codes are read as well to confirm that no errors have occurred since the data was written. If a single-bit error occurs, it can be corrected "on the fly". If this sounds similar to the way that ECC is used within hard disks today, that's for a good reason: it's pretty much exactly the same. It's also the same concept used for ECC protection of system memory.
    Level 2 is the only RAID level of the ones defined by the original Berkeley document that is not used today, for a variety of reasons. It is expensive and often requires many drives--see below for some surprisingly large numbers. The controller required was complex, specialized and expensive. The performance of RAID 2 is also rather substandard in transactional environments due to the bit-level striping. But most of all, level 2 was obviated by the use of ECC within a hard disk; essentially, much of what RAID 2 provides you now get for "free" within each hard disk, with other RAID levels providing protection above and beyond ECC.
    Due to its cost and complexity, level 2 never really "caught on". Therefore, much of the information below is based upon theoretical analysis, not empirical evidence.
    Controller Requirements: Specialized controller hardware required.
    Hard Disk Requirements: Depends on exact implementation, but a typical setup required 10 data disks and 4 ECC disks for a total of 14, or 32 data disks and 7 ECC disks for a total of 39! The disks were spindle-synchronized to run in tandem.
    Array Capacity: Depends on exact implementation but would be rather large if built today using modern drives.
    Storage Efficiency: Depends on the number of data and ECC disks; for the 10+4 configuration, about 71%; for the 32+7 setup, about 82%.
    Fault Tolerance: Only fair; for all the redundant drives included, you don't get much tolerance: only one drive can fail in this setup and be recoverable "on the fly".
    Availability: Very good, due to "on the fly" error correction.
    Degradation and Rebuilding: In theory, there would be little degradation due to failure of a single drive.
    Random Read Performance: Fair. Bit-level striping makes multiple accesses impossible.
    Random Write Performance: Poor, due to bit-level striping and ECC calculation overhead.
    Sequential Read Performance: Very good, due to parallelism of many drives.
    Sequential Write Performance: Fair to good.
    Cost: Very expensive.
    Special Considerations: Not used in modern systems.
    Recommended Uses: Not used in modern systems.
    __________________________________RAID3___________ ______________________
    RAID Level 3
    Common Name(s): RAID 3. (Watch out for some companies that say their products implement RAID 3 when they are really RAID 4.)
    Technique(s) Used: Byte-level striping with dedicated parity.
    Description: Under RAID 3, data is striped across multiple disks at a byte level; the exact number of bytes sent in each stripe varies but is typically under 1024. The parity information is sent to a dedicated parity disk, but the failure of any disk in the array can be tolerated (i.e., the dedicated parity disk doesn't represent a single point of failure in the array.) The dedicated parity disk does generally serve as a performance bottleneck, especially for random writes, because it must be accessed any time anything is sent to the array; this is contrasted to distributed-parity levels such as RAID 5 which improve write performance by using distributed parity (though they still suffer from large overheads on writes, as described here). RAID 3 differs from RAID 4 only in the size of the stripes sent to the various disks.

    Controller Requirements: Generally requires a medium-to-high-end hardware RAID card.
    Hard Disk Requirements: Minimum of three standard hard disks; maximum set by controller. Should be of identical size and type.
    Array Capacity: (Size of Smallest Drive) * (Number of Drives - 1)
    Storage Efficiency: If all drives are the same size, ( (Number of Drives - 1) / Number of Drives).
    Fault Tolerance: Good. Can tolerate loss of one drive.
    Availability: Very good. Hot sparing and automatic rebuild are usually supported by controllers that implement RAID 3.
    Degradation and Rebuilding: Relatively little degrading of performance if a drive fails. Rebuilds can take many hours.
    Random Read Performance: Good, but not great, due to byte-level striping.
    Random Write Performance: Poor, due to byte-level striping, parity calculation overhead, and the bottleneck of the dedicated parity drive.
    Sequential Read Performance: Very good.
    Sequential Write Performance: Fair to good.
    Cost: Moderate. A hardware controller is usually required, as well as at least three drives.
    Special Considerations: Not as popular as many of the other commonly-implemented RAID levels. For transactional environments, RAID 5 is usually a better choice.
    Recommended Uses: Applications working with large files that require high transfer performance with redundancy, especially serving or editing large files: multimedia, publishing and so on. RAID 3 is often used for the same sorts of applications that would typically see the use of RAID 0, where the lack of fault tolerance of RAID 0 makes it unacceptable.
    ___________________________________RAID4__________ ______________________
    RAID Level 4
    Common Name(s): RAID 4 (sometimes called RAID 3 by the confused).
    Technique(s) Used: Block-level striping with dedicated parity.
    Description: RAID 4 improves performance by striping data across many disks in blocks, and provides fault tolerance through a dedicated parity disk. This makes it in some ways the "middle sibling" in a family of close relatives, RAID levels 3, 4 and 5. It is like RAID 3 except that it uses blocks instead of bytes for striping, and like RAID 5 except that it uses dedicated parity instead of distributed parity. Going from byte to block striping improves random access performance compared to RAID 3, but the dedicated parity disk remains a bottleneck, especially for random write performance. Fault tolerance, format efficiency and many other attributes are the same as for RAID 3 and RAID 5.

    _Controller Requirements: Generally requires a medium-to-high-end hardware RAID card.
    Hard Disk Requirements: Minimum of three standard hard disks; maximum set by controller. Should be of identical size and type.
    Array Capacity: (Size of Smallest Drive) * (Number of Drives - 1).
    Storage Efficiency: If all drives are the same size, ( (Number of Drives - 1) / Number of Drives).
    Fault Tolerance: Good. Can tolerate loss of one drive.
    Availability: Very good. Hot sparing and automatic rebuild are usually supported..
    Degradation and Rebuilding: Moderate degrading if a drive fails; potentially lengthy rebuilds.
    Random Read Performance: Very good.
    Random Write Performance: Poor to fair, due to parity calculation overhead and the bottleneck of the dedicated parity drive.
    Sequential Read Performance: Good to very good.
    Sequential Write Performance: Fair to good.
    Cost: Moderate. A hardware controller is usually required, as well as at least three drives.
    Special Considerations: Performance will depend to some extent upon the stripe size chosen.
    Recommended Uses: Jack of all trades and master of none, RAID 4 is not as commonly used as RAID 3 and RAID 5, because it is in some ways a "compromise" between them that doesn't have a target market as well defined as either of those two levels. It is sometimes used by applications commonly seen using RAID 3 or RAID 5, running the gamut from databases and enterprise planning systems to serving large multimedia files.
    __________________________________RAID5___________ _____________________
    RAID Level 5
    Common Name(s): RAID 5.
    Technique(s) Used: Block-level striping with distributed parity.
    Description: One of the most popular RAID levels, RAID 5 stripes both data and parity information across three or more drives. It is similar to RAID 4 except that it exchanges the dedicated parity drive for a distributed parity algorithm, writing data and parity blocks across all the drives in the array. This removes the "bottleneck" that the dedicated parity drive represents, improving write performance slightly and allowing somewhat better parallelism in a multiple-transaction environment, though the overhead necessary in dealing with the parity continues to bog down writes. Fault tolerance is maintained by ensuring that the parity information for any given block of data is placed on a drive separate from those used to store the data itself. The performance of a RAID 5 array can be "adjusted" by trying different stripe sizes until one is found that is well-matched to the application being used.

    Controller Requirements: Requires a moderately high-end card for hardware RAID; supported by some operating systems for software RAID, but at a substantial performance penalty.
    Hard Disk Requirements: Minimum of three standard hard disks; maximum set by controller. Should be of identical size and type.
    Array Capacity: (Size of Smallest Drive) * (Number of Drives - 1).
    Storage Efficiency: If all drives are the same size, ( (Number of Drives - 1) / Number of Drives).
    Fault Tolerance: Good. Can tolerate loss of one drive.
    Availability: Good to very good. Hot sparing and automatic rebuild are usually featured on hardware RAID controllers supporting RAID 5 (software RAID 5 will require down-time).
    Degradation and Rebuilding: Due to distributed parity, degradation can be substantial after a failure and during rebuilding.
    Random Read Performance: Very good to excellent; generally better for larger stripe sizes. Can be better than RAID 0 since the data is distributed over one additional drive, and the parity information is not required during normal reads.
    Random Write Performance: Only fair, due to parity overhead; this is improved over RAID 3 and RAID 4 due to eliminating the dedicated parity drive, but the overhead is still substantial.
    Sequential Read Performance: Good to very good; generally better for smaller stripe sizes.
    Sequential Write Performance: Fair to good.
    Cost: Moderate, but often less than that of RAID 3 or RAID 4 due to its greater popularity, and especially if software RAID is used.
    Special Considerations: Due to the amount of parity calculating required, software RAID 5 can seriously slow down a system. Performance will depend to some extent upon the stripe size chosen.
    Recommended Uses: RAID 5 is seen by many as the ideal combination of good performance, good fault tolerance and high capacity and storage efficiency. It is best suited for transaction processing and is often used for "general purpose" service, as well as for relational database applications, enterprise resource planning and other business systems. For write-intensive applications, RAID 1 or RAID 1+0 are probably better choices (albeit higher in terms of hardware cost), as the performance of RAID 5 will begin to substantially decrease in a write-heavy environment.

    RAID6____________________________________________________

    RAID Level 6
    Common Name(s): RAID 6. Some companies use the term "RAID 6" to refer to proprietary extensions of RAID 5; these are not discussed here.
    Technique(s) Used: Block-level striping with dual distributed parity.
    Description: RAID 6 can be thought of as "RAID 5, but more". It stripes blocks of data and parity across an array of drives like RAID 5, except that it calculates two sets of parity information for each parcel of data. The goal of this duplication is solely to improve fault tolerance; RAID 6 can handle the failure of any two drives in the array while other single RAID levels can handle at most one fault. Performance-wise, RAID 6 is generally slightly worse than RAID 5 in terms of writes due to the added overhead of more parity calculations, but may be slightly faster in random reads due to spreading of data over one more disk. As with RAID levels 4 and 5, performance can be adjusted by experimenting with different stripe sizes

    Controller Requirements: Requires a specialized (usually meaning expensive) hardware controller.
    Hard Disk Requirements: Minimum of four hard disks; maximum set by controller. Should be of identical size and type.
    Array Capacity: (Size of Smallest Drive) * (Number of Drives - 2).
    Storage Efficiency: If all drives are the same size, ( (Number of Drives - 2) / Number of Drives).
    Fault Tolerance: Very good to excellent. Can tolerate the simultaneous loss of any two drives in the array.
    Availability: Excellent.
    Degradation and Rebuilding: Due to the complexity of dual distributed parity, degradation can be substantial after a failure and during rebuilding. Dual redundancy may allow rebuilding to be delayed to avoid performance hit.
    Random Read Performance: Very good to excellent; generally better for larger stripe sizes.
    Random Write Performance: Poor, due to dual parity overhead and complexity.
    Sequential Read Performance: Good to very good; generally better for smaller stripe sizes.
    Sequential Write Performance: Fair.
    Cost: High.
    Special Considerations: Requires special implementation; not widely available.
    Recommended Uses: In theory, RAID 6 is ideally suited to the same sorts of applications as RAID 5, but in situations where additional fault tolerance is required. In practice, RAID 6 has never really caught on because few companies are willing to pay for the extra cost to insure against a relatively rare event--it's unusual for two drives to fail simultaneously (unless something happens that takes out the entire array, in which case RAID 6 won't help anyway). On the lower end of the RAID 5 market, the rise of hot swapping and automatic rebuild features for RAID 5 have made RAID 6 even less desirable, since with these advanced features a RAID 5 array can recover from a single drive failure in a matter of hours (where without them, RAID 5 would require downtime for rebuilding, giving RAID 6 a substantial advantage.) On the higher end of the RAID 5 market, RAID 6 usually loses out to multiple RAID solutions such as RAID 10 that provide some degree of multiple-drive fault tolerance while offering improved performance as well.
    ________________________________RAID7_____________ _______________________

    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.
    ________________________________RAID10(1+0 or 0+1)_________________________
    RAID Levels 0+1 (01) and 1+0 (10)
    Common Name(s): RAID 0+1, 01, 0/1, "mirrored stripes", "mirror of stripes"; RAID 1+0, 10, 1/0, "striped mirrors", "stripe of mirrors". Labels are often used incorrectly; verify the details of the implementation if the distinction between 0+1 and 1+0 is important to you.
    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.

    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.
    Recommended Uses: Applications requiring both high performance and reliability and willing to sacrifice capacity to get them. This includes enterprise servers, moderate-sized database systems and the like at the high end, but also individuals using larger IDE/ATA hard disks on the low end. Often used in place of RAID 1 or RAID 5 by those requiring higher performance; may be used instead of RAID 1 for applications requiring more capacity.

    _______________________RAID0+3(03 or53)____________________

    RAID Levels 0+3 (03 or 53) and 3+0 (30)
    Common Name(s): The most confusing naming of any of the RAID levels. :^) In an ideal world, this level would be named RAID 0+3 (or 03) or RAID 3+0 (30). Instead, the number 53 is often used in place of 03 for reasons I have never been able to determine, and worse, 53 is often actually implemented as 30, not 03. As always, verify the details of the implementation to be sure of what you have.
    Technique(s) Used: Byte striping with dedicated parity combined with block striping.
    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.
    Array Capacity: For RAID 03: (Size of Smallest Drive) * (Number of Drives In Each RAID 0 Set) * (Number of RAID 0 Sets - 1). For RAID 30: (Size of Smallest Drive) * (Number of Drives In Each RAID 3 Set - 1) * (Number of RAID 3 Sets).
    For example, the capacity of a RAID 03 array made of 15 18 GB drives arranged as three five-drive RAID 0 sets would be 18 GB * 5 * (3-1) = 180 GB. The capacity of a RAID 30 array made of 21 18 GB drives arranged as three seven-drive RAID 3 sets would be 18 GB * (7-1) * 3 = 324 GB. The same 21 drives arranged as seven three-drive RAID 3 sets would have a capacity of 18 GB * (3-1) * 7 = "only" 252 GB.
    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.
    Recommended Uses: Not as widely used as many other RAID levels. Applications include data that requires the speed of RAID 0 with fault tolerance and high capacity, such as critical multimedia data and large database or file servers. Sometimes used instead of RAID 3 to increase capacity as well as performance.
    Resource: www.pcguide.com
    ALL THE BEST





    موضوعات مشابه:
    ویرایش توسط Beginner : 2009-12-07 در ساعت 08:06 AM
    darklove، reza_4247، narsis1367 و 3 نفر دیگر سپاسگزاری کرده‌اند.





  2. #2
    نام حقيقي: حسن رئیسی

    مسدود شده
    تاریخ عضویت
    Oct 2007
    محل سکونت
    تهران-ایران
    نوشته
    1,196
    سپاسگزاری شده
    507
    سپاسگزاری کرده
    105

    Post انواع RAID در سرورها ( قسمت دوم )

    RAID یا Redundant Array of Independent Disks :
    در صورتی که بخواهیم اطلاعات یک دیسک موجود در یک سرور یا هر دستگاه دیگری که بسیار مهم و حیاتی می باشند یک پشتیبان داشته باشیم از RAID استفاده می کنیم.
    در بسیاری از موارد پیش می آید که هارد دیسک مربوط به دستگاهی خراب می شود و در صورتی که آن دستگاه وظیفه مهمی در شبکه داشته باشد مسلما با مشکل مواجه می شویم. به طور مثال فرض کنید که سرور مربوط AD هارد آن خراب شود. در این صورت می توان گفت عملا کار شبکه مختل خواهد شد و بسیاری مشکلات به وجود خواهد آمد. حال اگر سیستم RAID بر روی هارد دیسکهای یک دستگاه فعال شود می توانیم از این مشکل جلوگیری نماییم. با این کار ما Fault Telorance را برای هارد دیسک ایجاد کرده ایم.
    در ابتدا هارد دیسکها 2 حالت دارند :
    1) Basic Mode
    2) Dynamic Mode
    زمانی که به اصطلاح ما از قدیم هارد خود را با دستور fdisk پارتیشن بندی می کردیم و یا با خود ویندوز و هر برنامه دیگری الان پارتیشن بندی می کنیم هار دیسک ما به صورت عادی حالت Basic می باشد.
    در حالت Basic ما به هر یک از درایو ها اصطلاحا Partition می گوییم ولی در حالت Dynamic به آن Volume گفته می شود.
    هر یک از دو حالتی که در بالا گفته شد دارای تقسیم بندی هستند که در زیر گفته شده است.
    Basic Mode :
    در این حالت ما موارد زیر را داریم :
    - Primary Partition
    - Extended Partition
    - Logical Drive
    Dynamic Mode:
    در حالت Dynamic یا پویا موارد زیر می باشند :
    - Simple Volume
    - Spanned Volume
    - RAID 0 - Stripped Volume
    - RAID 1 – Mirror Volume
    - RAID 5 - Stripped with parity
    * هر گاه یک هارد دیسک را از حالت Basic Mode به Dynamic Mode تبدیل کنیم ، تمامی پارتیشن های آن به Simple Volume تبدیل خواهند شد و قابلیت بازگشت به Basic Mode دیگر وجود ندارد.
    Simple Volume :
    ساده ترین نوع Volume می باشد. این نوع Volume قابلیت Extend شدن دارد. در این حالت ما Fault Telorance نداریم و امکان از بین رفتن اطلاعات وجود دارد.
    Spanned Volume :
    برای راه اندازی Spanned Volume باید حداقل 2 تا هارد دیسک و حداکثر 32 هارد دیسک داشته باشیم. اگر درایو جدیدی در این حالت بخواهیم بسازیم ، از فضای تمامی دیسکها استفاده می کند و مثلا درایو H را می سازد.
    در این حالت در هنگام نوشتن اطلاعات ابتدا هارد دیسک اول پر می شود و سپس به سراغ دیسک دیگر می رود و به همین ترتیب ادامه می دهد. اگر یکی از هارد دیسکهای Spanned Volume ، از کار بیفتد و یا بسوزد کل آن درایو از بین خواهد رفت ، پس در این حالت هم ما Fault Telorance نداریم.
    تمام این مطالب گفته شد تا مبحث RAID که در اینجا تازه شروع می شود بیشتر جا بیفتد.
    RAID چیست؟
    RAID مخفف عبارت Redundant Arraye of Independent Disks است برای اولین بار در سال 1988 طی مقاله ای که توسط 3 محقق دانشگاه برکلی به نام های Patterson ، Gibson و Katz معرفی شد. در این مقاله پیکربندی آرایه ای و برنامه ای ،برای چندین هارد دیسک ارزان قیمت برای داشتن قابلیت Fault Telorance یا همان کاهش نرخ خطا و همچنین بهبود و افزایش نرخ دسترسی داده ها مهیا شد.
    RAID قابلیت دسترسی چندگانه به چند دیسک به طور همزمان را مهیا می کند و این باعث می شود که ابتدا خطر از دست دادن اطلاعات که قبلا بر روی یک دیسک بود از بین برود و همچنین زمان دسترسی بهبود یابد.
    به طور معمول RAID در فایل سرور های بزرگ ، تراکنش در سرورهای برنامه های کاربردی زمانی که Fault Telorance و زمان دسترسی اهمیت دارد استفاده می شود اما امروزه در کامپیوترهای رومیزی برای نرم افزارهایی همچون CAD ، نرم افزارهای ویرایش فایل های چندرسانه ای زمانی که نرخ انتقال داده ها بسیار زیاد است استفاده می شود.
    RAID 0 یا Stripped Volume :
    این مورد همان قابلیتهای Spanned را دارد با این فرق که اطلاعات به صورت مساوی در بین دیسکها تقسیم می شود و این حالت Performance یا کارایی را برای Read خواندن و Write نوشتن بهبود می بخشد.
    RAID 1 یا Mirror Volume :
    این حالت متشکل از 2 هارد دیسک می باشد. هر درایوی را که بخواهیم می توانیم Mirror کنیم. در این حالت کپی عینی از اطلاعات یک دیسک در دیسک دیگر قرار می گیرد و با از کار افتادن یکی از دیسکها ، دیسک دیگر کار خود را به عنوان جایگزین با در اختیار داشتن تمامی اطلاعات انجام می دهد. در این حالت بالاترین قابلیت Fault Telorance را شاهد هستیم.
    RAID 3 یا Disk Stripping With Dedicated Parity Disk :
    در این حالت اطلاعات بین 2 درایو تقسیم می شوند. در کنار 2 درایو ، درایو دیگری فقط جهت نگه داشتن parity یا بیت توازن جهت تصحیح خطاها و بازیابی آنها در نظر گرفته می شود. این حالت بیشتر برای برنامه هایی که انتقال داده یکطرفه با نرخ بالا دارند استفاده میشود. این برنامه ها معمولا شامل موارد زیر می شوند:
    - پردازنده های تشخیص گرافیکی ، فایلهای CAD و CAM و …
    - برنامه های بدون غیرتراکنشی که حجم داده های ترتیبی بزرگی را پردازش می کنند.
    * قابل توجه است که برای این حالت حداقل به 3 درایو نیاز است.
    RAID 5 یا Stripped with Parity :
    در این حالت حداقل 3 هارد دیسک و حداکثر 32 دیسک می توانیم داشته باشیم. همچنین در این حالت Parity ها به صورت تصادفی در دیسک های مختلف نوشته می شوند و با از دست دادن یک دیسک می توانیم با اضافه کردن دیسک جدید و جایگزین به صورت اتوماتیک هار دیسک دیگر ساخته و محاسبه و تکمیل گردد. در این حالت هر چه تعداد هارد دیسکها بیشتر باشد ، تلفات اطلاعاتی کمتر خواهد بود و اگر کاملا یک هارد را از دست بدهیم ، برخی اطلاعات برگردانده و ساخته می شود و برخی دیگر از دست می رود که با زیاد بودن این هارد دیسکها ، مقدار اطلاعاتی که از دست میرود کمتر خواهد بود.
    * پیشنهاد می دهم که جاهایی که File Server و SQL یا بطور کل Database داریم از RAID 5 استفاده شود.
    اخیرا دو RAID دیگر هم به مجموعه RAID ها اضافه شده است که تحت عنوان RAID 6 و RAID TP شناخته می شوند.
    در اینجا چون پست خیلی طولانی شد و بنده نویسنده هم خسته شدم ، در مورد RAID 6 و RAID TP در پست بعدی صحبت خواهم کرد.
    به عنوان آخرین نکته در نظر داشته باشید که RAID در کل به دو صورت نرم افزاری و سخت افزاری قابل پیاده سازی می باشد. که در حالت سخت افزاری یک Slot یا درگاه جداگانه برای آن در نظر گرفته می شود و معمولا تحت عنوان RAID Controller شناخته می شود.

    RAID 6 یا Disk Striping with Double Distributed Parity :
    RAID 6 بلوکهای اطلاعاتی و همچنین بیت توازن (Parity) را همانند RAID 5 در یک آرایه تقسیم می کند. در RAID 6 به جای یک بیت توازن دو مجموعه از بیت های توازن اطلاعاتی را برای هر گروه از داده نگهداری می کند. نتیجه این عمل بهبود آرایه های تلرانس خطا می باشد. RAID 6 در عمل هنگام نوشتن بیت های توازن دارای سرعت کمتری نسبت به RAID 5 باشد اما در هنگام خواندن اطلاعات به صورت تصادفی بسیار سبکتر و سریعتر در بین اطلاعات منتشر شده در بیش از یک دیسک نسبت به RAID 5 خواهد بود.
    RAID 6 حداقل به 4 درایو جهت پیاده سازی نیاز دارد.
    مزایا:
    داده روی یک سطح بلوک در میان یک مجموعه از درایوها به همان روش همانند RAID 5 تقسیم می شود ولی در دومین مجموعه از بیت توازن محاسبه و همچنین نوشتن در سرتاسر تمامی درایوها انجام می شود. RAID 6 تلرانس خطا و همچنین تلرانس خرابی درایو را پیشنهاد می دهد.همچنین تحمل از کار افتادن همزمان چندین درایو را برای ماموریت برنامه های حیاتی را به صورت ایده آل فراهم می کند.
    معایب:
    RAID 6 به یک کنترلر کامل برای پیاده سازی و جبران کردن سربار محاسبه بیت توازن دو تایی نیاز دارد. همچنین به N+2 درایو برای پیاده سازی ساختار دو بعدی بیت توازن احتیاج دارد. از نو بنا کردن ای حالت به طور مشخص بر روی کارایی سیستم تاثیر خواهد داشت.
    برنامه های کاربردی پیشنهادی بر روی این حالت:
    نگهداری و ذخیره سازی سازمانها
    گرفتن نسخه پشتیبان دیسک به دیسک
    نرم افزارهایی ویدئویی با کارایی کیفیت بسیار بالا
    پشتیبان گیری ثابت محتوا یا آرشیوی
    مقبولیت قوانین ذخیره سازی
    فاجعه ذخیره بازیابی اطلاعات

    شبکه های کامپیوتری ، نتورک پروف ، آموزش شبکه ، RAID 6

    RAID TP یا Disk Striping with Triple Distributed Parity:
    همانند RAID 5 و RAID 6 ، در RAID TP داده در بین درایوها تقسیم می شود اما محاسبات برای 3 بیت توازن برای نوشتن در 3 دیسک خاص انجام می شود. RAID TP از 3 معادله همچندی برای محاسبه هر بیت توازن خاص که دوباره سازی اطلاعات را در زمانی که 3 دیسک یا بلوک در یک زمان خراب شوند استفاده می کند.
    RAID TP یک سطح اضافی از افزونگی را برای محافظت از داده های شما مهیا می کند.
    برنامه های کاربردی پیشنهادی بر روی این حالت:

    • نگهداری و ذخیره سازی سازمانها
    • گرفتن نسخه پشتیبان دیسک به دیسک
    • نرم افزارهایی ویدئویی با کارایی کیفیت بسیار بالا
    • پشتیبان گیری ثابت محتوا یا آرشیوی
    • مقبولیت قوانین ذخیره سازی
    • فاجعه ذخیره بازیابی اطلاعات

    * RAID TP برای پیاده سازی حداقل به 4 درایو نیاز دارد.



    ARM، jooya، peyman13618 و 10 نفر دیگر سپاسگزاری کرده‌اند.

  3. #3
    نام حقيقي: حسن رئیسی

    مسدود شده
    تاریخ عضویت
    Oct 2007
    محل سکونت
    تهران-ایران
    نوشته
    1,196
    سپاسگزاری شده
    507
    سپاسگزاری کرده
    105
    اینم برای Recover کردن

    ftp://download.intel.com/support/mot...cover_proc.pdf


    sma.ffcc و tamia سپاسگزاری کرده‌اند.

کلمات کلیدی در جستجوها:

انواع raid

raid انواعانواع ریدهاتحقیق در مورد raidانواع RAID در سرورهامقاله RAIDمقاله درباره raidانواع raid pdfمقاله در مورد raidانواعRAIDدر مورد rAidانواع مقالهraidانواع radesearch انواع سنگهامقاله ای در مورد RAIDانواع درانواع سنگهاhttp://forum.persiannetworks.com/f78/t30183.htmlraidانواعدرباره raidموضوع مقالهraid 6 دربارهمقاله ای در باره پروانه هاraid تحقیق

برچسب برای این موضوع

مجوز های ارسال و ویرایش

  • شما نمی توانید موضوع جدید ارسال کنید
  • شما نمی توانید به پست ها پاسخ دهید
  • شما نمی توانید فایل پیوست ضمیمه کنید
  • شما نمی توانید پست های خود را ویرایش کنید
  •