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RAID Definitions

This is an explanation of RAID and the 3 levels of RAID that we typically use.  RAID definitions of the RAID levels used by Cbeyond Cloud Servers.  
 

RAID 1 - Disk Mirroring

 

Definition

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Data is written to a primary disk and a secondary disk.  Identical data is stored on both disks.

 

Redundancy

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A mirrored set of drives is created.  One can be lost.

 

Performance

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High performance in read intensive applications.  If one drive is busy data can be accessed from the secondary disk.  High write performance because of no parity overhead.

 

Drawbacks

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High cost per megabyte because double the amount of drives is required to achieve desired capacity.

 

Comparison

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Faster than RAID 5, similar in speed to RAID 10, however not as much expandability as RAID 10, limited to 2 drives and 2 drives only.

 

Recommendations

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Recommended for standard application servers, AD, DNS, and any other base, entry level application that 2 drives will suffice.

 

 

RAID 5 - Data Striping with Distributed Parity

 

Definition

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Data is striped across a group of disk drives with distributed parity.  Parity information is written to a different disk in the array for each stripe.

 

Redundancy

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Parity is distributed across the disks in the array.  Data is regenerated in the event of a drive failure.

 

Performance

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High performance in small record, multiprocessing environments because there is no contention for the parity disk and read and write operations can be overlapped.

 

Drawbacks

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Distributed parity causes overhead on write operations. There is also overhead created when data is changed, because parity information must be located and then recalculated.

 

Comparison

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Considerably slower than RAID 1 or 10, however can grow larger than RAID 10 with fewer drives.  6 drive chassis will have more usable capacity when full with RAID 5 over RAID 10. 

 

Recommendations

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Recommended for file servers that will store data but will not change the data on a regular basis.

 

 

RAID 10 or 0+1 - Data Striping with Mirroring

 

Definition

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RAID 10 is a combination of RAID levels 0 and 1 by striping data across pairs of mirrored disk drives.

 

Redundancy

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A striped array (RAID 0) of mirrored drive pairs (RAID 1) is created.  You can sustain more than one drive failure as long as they are not in the same mirrored set, however only guarantees one drive of redundancy.

 

Performance

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High performance because data is striped and there is no parity overhead. More spindles to read and write data gives greater increase especially when paired with SAS drives.

 

Drawbacks

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High cost per megabyte because double the amount of drives is required to achieve desired capacity.

 

Comparison

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Faster than RAID 5, more expandable than RAID 1 and may provide slightly more redundancy.  RAID 5 can grow larger with the same number of disks but is slower.

 

Recommendations

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Recommended for any database type server, SQL, MS Exchange, etc. where read & write speeds are imperative and more drives are needed to achieve size or redundancy needs.

Article ID: 787, Created On: 5/4/2011, Modified: 5/4/2011

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