RAID-Definitions
 | | RAID Level 0 requires a minimum of 2 drives to implement |  Advantages |  Disadvantages | RAID 0 implements a striped disk array, the data is broken down into blocks and each block is written to a separate disk drive
No parity calculation overhead is involved
Very simple design
Easy to implement | 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 |
 | | RAID Level 1 requires a minimum of 2 drives to implement | | Advantages | Disadvantages | One Write or two Reads possible per mirrored pair
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 | 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. |
 | | 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. | | Advantages | Disadvantages | 'On the fly' data error correction
Extremely high data transfer rates possible
The higher the data transfer rate required, the better the ratio of data disks to ECC disks | 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. |
 | 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 | | Advantages | Disadvantages | Very high Read data transfer rate
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 | 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 |
 | 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 | | Advantages | Disadvantages | Very high Read data transaction rate
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 | 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 |
 | | 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 | | Advantages | Disadvantages | Highest Read data transaction rate
Medium Write data transaction rate
Low ratio of ECC (Parity) disks to data disks means high efficiency
Good aggregate transfer rate | 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 |
 | | 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 | | Advantages | Disadvantages | RAID 6 is essentially an extension of RAID level 5 which allows for additional fault tolerance by using a second independent distributed parity scheme (two-dimensional parity)
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 | 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 |
 | Fully implemented process oriented real time operating system resident on embedded array control microprocessor.
RAID 7 is a registered trademark of Storage Computer Corporation. | | Advantages | Disadvantages | Overall write performance is 25% to 90% better than single spindle performance and 1.5 to 6 times better than other array levels
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 | 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 |
 | | RAID Level 10 requires a minimum of 4 drives to implement | | Advantages | Disadvantages | RAID 10 is implemented as a striped array whose segments are RAID 1 arrays
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 | 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 |
 | | RAID Level 53 requires a minimum of 5 drives to implement | | Advantages | Disadvantages | RAID 53 should really be called 'RAID 03' because it is implemented as a striped (RAID level 0) array whose segments are RAID 3 arrays
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 | 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 |
 | | RAID Level 0+1 requires a minimum of 4 drives to implement | | Advantages | Disadvantages | RAID 0+1 is implemented as a mirrored array whose segments are RAID 0 arrays
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 | 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 |
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