RAID 0 : Striped Disk Array without Fault Tolerance

RAID 1 : Mirroring and Duplexing

RAID 2 : Hamming Code ECC

RAID 3 : Parallel transfer with parity

RAID 4 : Independent Data disks with shared Parity disk

RAID 5 : Independent Data disks with distributed parity blocks

RAID 6 : Independent Data disks with two independent distributed parity schemes

RAID 7 : Optimized Asynchrony for High I/O Rates as well as High Data Transfer Rates

RAID 10 : Very High Reliability combined with High Performance

RAID 53 : High I/O Rates and Data Transfer Performance

RAID 0+1 : High Data Transfer Performance





RAID 0 : Striped Disk Array without Fault Tolerance


". "No parity calculation overhead is involved"."

". "Very simple design"."

". "Easy to implement"; $strContra = "Not a 'True' RAID because it is NOT fault-tolerant"."

". "The failure of just one drive will result in all data in an array being lost"."

". "Should never be used in mission critical environments"; print_pro_contra("/images/raid/raid0.gif","RAID Level 0 requires a minimum of 2 drives to implement",$strPro,$strContra); ?>


RAID 1 : Mirroring and Duplexing


". "100% redundancy of data means no rebuild is necessary in case of a disk failure, just a copy to the replacement disk"."

". "Simplest RAID storage subsystem design"; $strContra = "Highest disk overhead of all RAID types (100%) - inefficient"."

". "Typically the RAID function is done by system software, loading the CPU/Server and possibly degrading throughput at high activity levels. Hardware implementation is strongly recommended."; print_pro_contra("/images/raid/raid1.gif","RAID Level 1 requires a minimum of 2 drives to implement",$strPro,$strContra); ?>


RAID 2 : Hamming Code ECC


". "Extremely high data transfer rates possible"."

". "The higher the data transfer rate required, the better the ratio of data disks to ECC disks"; $strContra = "Very high ratio of ECC disks to data disks with smaller word sizes - inefficient"."

". "Entry level cost very high - requires very high transfer rate requirement to justify."."

". "No commercial implementations exist."; $strIntro = "Each bit of data word is written to a data disk drive (4 in this example: 0 to 3). Each data word has its Hamming Code ECC word recorded on the ECC disks. On Read, the ECC code verifies correct data or corrects single disk errors."; print_pro_contra("/images/raid/raid2.gif",$strIntro,$strPro,$strContra); ?>


RAID 3 : Parallel transfer with parity


". "Very high Write data transfer rate"."

". "Disk failure has an insignificant impact on throughput"."

". "Low ratio of ECC (Parity) disks to data disks means high efficiency"; $strContra = "Transaction rate equal to that of a single disk drive at best (if spindles are synchronized)"."

". "Controller design is fairly complex"."

". "Very difficult and resource intensive to do as a 'software' RAID"; $strIntro = "The data block is subdivided ('striped') and written on the data disks. Stripe parity is generated on Writes, recorded on the parity disk and checked on Reads.
". "RAID Level 3 requires a minimum of 3 drives to implement"; print_pro_contra("/images/raid/raid3.gif",$strIntro,$strPro,$strContra); ?>


RAID 4 : Independent Data disks with shared Parity disk


". "Low ratio of ECC (Parity) disks to data disks means high efficiency"."

". "High aggregate Read transfer rate"."

". "Low ratio of ECC (Parity) disks to data disks means high efficiency"; $strContra = "Quite complex controller design"."

". "Worst Write transaction rate and Write aggregate transfer rate"."

". "Difficult and inefficient data rebuild in the event of disk failure"."

". "Block Read transfer rate equal to that of a single disk"; $strIntro = "Each entire block is written onto a data disk. Parity for same rank blocks is generated on Writes, recorded on the parity disk and checked on Reads.
". "RAID Level 4 requires a minimum of 3 drives to implement"; print_pro_contra("/images/raid/raid4.gif",$strIntro,$strPro,$strContra); ?>


RAID 5 : Independent Data disks with distributed parity blocks


". "Medium Write data transaction rate"."

". "Low ratio of ECC (Parity) disks to data disks means high efficiency"."

". "Good aggregate transfer rate"; $strContra = "Disk failure has a medium impact on throughput"."

". "Most complex controller design"."

". "Difficult to rebuild in the event of a disk failure (as compared to RAID level 1)"."

". "Individual block data transfer rate same as single disk"; $strIntro = "Each entire data block is written on a data disk; parity for blocks in the same rank is generated on Writes, recorded in a distributed location and checked on Reads.". "RAID Level 5 requires a minimum of 3 drives to implement"; print_pro_contra("/images/raid/raid5.gif",$strIntro,$strPro,$strContra); ?>


RAID 6 : Independent Data disks with two independent distributed parity schemes


". "Data is striped on a block level across a set of drives, just like in RAID 5, and a second set of parity is calculated and written across all the drives; RAID 6 provides for an extremely high data fault tolerance and can sustain multiple simultaneous drive failures"."

". "Perfect solution for mission critical applications"; $strContra = "Very complex controller design"."

". "Controller overhead to compute parity addresses is extremely high"."

". "Very poor write performance"."

". "Requires N+2 drives to implement because of two-dimensional parity scheme"; $strIntro = "Each entire data block is written on a data disk; parity for blocks in the same rank is generated on Writes, recorded in a distributed location and checked on Reads.". "RAID Level 5 requires a minimum of 3 drives to implement"; print_pro_contra("/images/raid/raid6.gif",$strIntro,$strPro,$strContra); ?>


RAID 7 : Optimized Asynchrony for High I/O Rates as well as High Data Transfer Rates


". "Host interfaces are scalable for connectivity or increased host transfer bandwidth"."

". "Small reads in multi user environment have very high cache hit rate resulting in near zero access times"."

". "No extra data transfers required for parity manipulation"; $strContra = "One vendor proprietary solution"."

". "Extremely high cost per MB"."

". "Very short warranty"."

". "Not user serviceable"."

". "Power supply must be UPS to prevent loss of cache data"; $strIntro = "Fully implemented process oriented real time operating system resident on embedded array control microprocessor.". "
RAID 7 is a registered trademark of Storage Computer Corporation."; print_pro_contra("/images/raid/raid7.gif",$strIntro,$strPro,$strContra); ?>


RAID 10 : Very High Reliability combined with High Performance


". "RAID 10 has the same fault tolerance as RAID level 1"."

". "RAID 10 has the same overhead for fault-tolerance as mirroring alone"."

". "Excellent solution for sites that would have otherwise gone with RAID 1 but need some additional performance boost"; $strContra = "Very expensive / High overhead"."

". "All drives must move in parallel to proper track lowering sustained performance"."

". "Very limited scalability at a very high inherent cost"; $strIntro = "RAID Level 10 requires a minimum of 4 drives to implement"; print_pro_contra("/images/raid/raid10.gif",$strIntro,$strPro,$strContra); ?>


RAID 53 : High I/O Rates and Data Transfer Performance


". "RAID 53 has the same fault tolerance as RAID 3 as well as the same fault tolerance overhead"."

". "High data transfer rates are achieved thanks to its RAID 3 array segments"."

". "Maybe a good solution for sites who would have otherwise gone with RAID 3 but need some additional performance boost"; $strContra = "Very expensive to implement"."

". "All disk spindles must be synchronized, which limits the choice of drives"."

". "Byte striping results in poor utilization of formatted capacity"; $strIntro = "RAID Level 53 requires a minimum of 5 drives to implement"; print_pro_contra("/images/raid/raid53.gif",$strIntro,$strPro,$strContra); ?>


RAID 0+1 : High Data Transfer Performance


". "RAID 0+1 has the same fault tolerance as RAID level 5"."

". "RAID 0+1 has the same overhead for fault-tolerance as mirroring alone"."

". "Excellent solution for sites that need high performance but are not concerned with achieving maximum reliability "; $strContra = "RAID 0+1 is NOT to be confused with RAID 10. A single drive failure will cause the whole array to become, in essence, a RAID Level 0 array"."

". "Very expensive / High overhead"."

". "Very limited scalability at a very high inherent cost"."

". "All drives must move in parallel to proper track lowering sustained performance"; $strIntro = "RAID Level 0+1 requires a minimum of 4 drives to implement"; print_pro_contra("/images/raid/raid01.gif",$strIntro,$strPro,$strContra); ?>



(c) Advanced Computer & Network Corporation ". "". "". "". "". "". "".$strMin. "". "". "". "". "Advantages". "". "Disadvantages". "". "". "".$strPro."". "".$strContra."". "". ""; } print_footer($urlThisPage,$strSection,$strSubSection,$nu); ?>