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RAID: An In-Depth Guide To RAID Technology

RAID 0

RAID Level 0 requires a minimum of 2 drives to implement

Characteristics and Advantages
  • RAID 0 implements a striped disk array, the data is broken down into blocks and each block is written to a separate disk drive
  • I/O performance is greatly improved by spreading the I/O load across many channels and drives
  • Best performance is achieved when data is striped across multiple controllers with only one drive per controller
  • No parity calculation overhead is involved
  • Very simple design
  • Easy to implement
Disadvantages
  • 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
Recommended Applications
  • Video Production and Editing
  • Image Editing
  • Pre-Press Applications
  • Any application requiring high bandwidth
Recommended Products
  • JetStor SATA 416S
  • JetStor SATA 412S
  • JetStor SATA 316F
RAID 1

For Highest performance, the controller must be able to perform two concurrent separate Reads per mirrored pair or two duplicate Writes per mirrored pair.

RAID Level 1 requires a minimum of 2 drives to implement

Characteristics and Advantages
  • One Write or two Reads possible per mirrored pair
  • Twice the Read transaction rate of single disks, same Write transaction rate as single disks
  • 100% redundancy of data means no rebuild is necessary in case of a disk failure, just a copy to the replacement disk
  • Transfer rate per block is equal to that of a single disk
  • Under certain circumstances, RAID 1 can sustain multiple simultaneous drive failures
  • Simplest RAID storage subsystem design
Disadvantages
  • 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
  • May not support hot swap of failed disk when implemented in "software"
Recommended Applications
  • Accounting
  • Payroll
  • Financial
  • Any application requiring very high availability
RAID 0+1

RAID Level 0+1 requires a minimum of 4 drives to implement

Characteristics and Advantages
  • 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
  • High I/O rates are achieved thanks to multiple stripe segments
  • Excellent solution for sites that need high performance but are not concerned with achieving maximum reliability
Disadvantages
  • 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
  • All drives must move in parallel to proper track lowering sustained performance
  • Very limited scalability at a very high inherent cost
Recommended Applications
  • Imaging applications
  • General fileserver
Recommended Products
  • JetStor SATA 416S
  • JetStor SATA 412S
  • JetStor SATA 316F
RAID 2

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.

Characteristics and Advantages
  • 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
  • Relatively simple controller design compared to RAID levels 3,4 & 5
Disadvantages
  • 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
  • Transaction rate is equal to that of a single disk at best (with spindle synchronization)
  • No commercial implementations exist / not commercially viable
RAID 3

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

Characteristics and Advantages
  • 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
Disadvantages
  • 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
Recommended Applications
  • Video Production and live streaming
  • Image Editing
  • Video Editing
  • Prepress Applications
  • Any application requiring high throughput
Recommended Products
  • JetStor SATA 416S
  • JetStor SATA 412S
  • JetStor SATA 316F
RAID 4

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

Characteristics and Advantages
  • Very high Read data transaction rate
  • Low ratio of ECC (Parity) disks to data disks means high efficiency
  • High aggregate Read transfer rate
Disadvantages
  • 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
RAID 5

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

Characteristics and Advantages
  • 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
Disadvantages
  • 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
Recommended Applications
  • File and Application servers
  • Database servers
  • Web, E-mail, and News servers
  • Intranet servers
  • Most versatile RAID level
Recommended Products
  • JetStor SATA 416S
  • JetStor SATA 412S
  • JetStor SATA 316F
RAID 6
  • 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
Disadvantages
  • More complex controller design
  • Controller overhead to compute parity addresses is extremely high
  • Write performance can be brought on par with RAID Level 5 by using a custom ASIC for computing Reed-Solomon parity
  • Requires N+2 drives to implement because of two-dimensional parity scheme
RAID 10

RAID Level 10 requires a minimum of 4 drives to implement

Characteristics & Advantages
  • 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
  • High I/O rates are achieved by striping RAID 1 segments
  • Under certain circumstances, RAID 10 array can sustain multiple simultaneous drive failures
  • Excellent solution for sites that would have otherwise gone with RAID 1 but need some additional performance boost
Disadvantages
  • 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
Recommended Applications
  • Database server requiring high performance and fault tolerance
RAID 50

RAID Level 50 requires a minimum of 5 drives to implement.

Characteristics & Advantages
  • RAID 50 should really be called "RAID 03" because it is implemented as a striped (RAID level 0) array whose segments are RAID 3 arrays
  • RAID 50 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
  • High I/O rates for small requests are achieved thanks to its RAID 0 striping
  • Maybe a good solution for sites who would have otherwise gone with RAID 3 but need some additional performance boost
Disadvantages
  • 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
Recommended RAID Products
  • JetStor SATA 416S
  • JetStor SATA 412S
  • JetStor SATA 316F
This RAID Tutorial is provided compliments of Advanced Computer & Network Corporation Advanced Computer & Network Corporation designs, manufactures and markets high-performance, competitively priced data storage RAID systems. For more information, go to www.acnc.com



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11/21/17
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