The Ultimate Guide for RAID

Data loss for anyone whether it is a business or individual ultimately means lost business or shattered memories respectively. Data is the most valuable asset of any business, and this can’t be understated, protection of business assets must always command the highest priority.

Backing up data will not be enough if you have no protection against online disk failure. Adding RAID to your storage configuration is the most cost effective and simplest ways to maintain access and data protection.

raid1

Whilst a number of companies offer RAID, not all RAID implementation are created equal. As an example there is Hardware RAID which is determined by a specific RAID controller which will probably have Cache memory as well to boost performance and possible battery back-up in case the controller fails. Hardware RAID has history and is very mature. Software RAID on the other hand is not totally new but the quality and reliability is dictated by the quality of the components used in the integration of the RAID components and the quality of software code driving the RAID implementation.

To choose the RAID level that’s right for you, begin by considering the factors below. Each one of these factors becomes a trade-off for another:

 

The Cost basically comes down to the trade-off between disk capacity and added data availability or performance. For example, RAID 1,10 and small disk counts of RAID 6 are costly in terms of lost disk space (50%), but high in data availability.

Performance also depends on the access pattern (random/sequential, read/write, long/short) and the numbers of users. Our guide is intended to give an overview on the performance and availability of various RAID levels in general and may not be accurate in all user scenarios. This is meant only as a guide through the RAID jungle.

The following are commonly used RAID levels:


Min # Drives:
2
Read/Write Speed:
High/High
Capacity Utilization:
100%
Typical Applications:
High End Workstations, data logging, real-time rendering, very transitory data
raid0-table

Definition

Striping without parity, improved performance, additional storage, no fault tolerance

Advantages

  • 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 channels with only one drive per channel)
  • No parity calculation overhead is involved
  • Very simple design
  • Easy to implement

Disadvantages

  • Not a “True” RAID because the failure of just one drive will result in all data in a virtual disk being lost
  • Should not be used for critical data


Min # Drives:
2
Read/Write Speed:
High/Medium
Capacity Utilization:
50%
Typical Applications:
Operating System, transaction databases
raid1-table

Definition

Mirroring without parity, fault tolerance for disk errors and single disk failures

Advantages

  • High performance up to twice the read transaction rate of single disks, and the same write transaction rate as single disks
  • 100 percent redundancy of data means no rebuild of data is necessary in case of disk failure, just a copy to the replacement disk
  • Typically supports hot-swap disks
  • Simplest RAID storage subsystem design

Disadvantages

  • Highest disk overhead of all RAID types (100 percent) results in inefficient use of drive capacity
  • Limited capacity since the virtual disk can only include two disk drives


Min # Drives:
3
Read/Write Speed:
High/Low
Capacity Utilization:
67%-94%
Typical Applications:
Data warehousing, web serving, archiving
raid5-table

Definition

Striping with distributed parity, improved performance, fault tolerance for disk errors and single disk failures

Advantages

  • Most efficient use of drive capacity of all the redundant RAID configurations
  • High read transaction rate
  • Medium-to-high write transaction rate

Disadvantages

  • Disk failure has a medium impact on throughput
  • Most complex controller design
  • Retrieval of parity information after a drive failure takes longer than with mirroring


Min # Drives:
4
Read/Write Speed:
High/Low
Capacity Utilization:
50%-88%
Typical Applications:
High End Workstations, data logging, real-time rendering, very transitory data
raid6-table

Definition

Striping with dual parity, fault tolerance for dual drive failures

Advantages

  • Can survive the loss of two disks without losing data
  • Data redundancy, high read rates, and good performance

Disadvantages

  • Requires two sets of parity data for each write operation, resulting in significant decrease in write performance
  • Additional costs because of the extra capacity required by using two parity blocks per stripe
  • Retrieval of parity information after a drive failure takes longer than with mirroring


Min # Drives:
4
Read/Write Speed:
High/Medium
Capacity Utilization:
50%
Typical Applications:
Fast databases, application servers
raid10-table

Definition

Implements a 1+0 RAID Level, enabling block level and mirroring combined with striping, better performance, fault tolerance for disk errors and multiple drive failure (one drive failure per mirror set)

Advantages

  • RAID 10 has the same redundancy as RAID level 1
  • High I/O rates are achieved by striping RAID 1 segments

Disadvantages

  • Most expensive RAID solution
  • Requires 2n where n > 1 disks
  • Very limited scalability at a very high inherent cost


Min # Drives:
6
Read/Write Speed:
High/Medium
Capacity Utilization:
67%-94%
Typical Applications:
Large databases, file servers, application servers
raid50-table

Definition

Combines multiple RAID 5 sets with striping, improved performance, fault disk errors and multiple drive failures (one drive failure per span)

Advantages

  • Allows creation of largest RAID groups, up to 256 drives (theoretical)
  • High read transaction rate
  • Higher degree of fault tolerance due to parity calculation being done for each RAID 5 subset
  • Potential for faster read transaction rates over large RAID 5 virtual disks
  • Medium-to-high write transaction rate

Disadvantages

  • Potential for faster read transaction rates over large RAID 5 virtual disks
  • One of the more complex RAID implementations
  • Less space efficient than RAID 5 since separate parity calculations are done for each RAID 5 subset
  • Retrieval of parity information after a drive failure takes longer than using a mirrored solution


Min # Drives:
8
Read/Write Speed:
High/Medium
Capacity Utilization:
50%-88%
Typical Applications:
Data archive, backup to disk, high availability solutions, servers with large capacity requirements
raid60-table

Definition

Combines multiple RAID 6 sets with striping, improved performance, fault disk errors and multiple drive failures (two drive failures per span)

Advantages

  • Allows creation of largest RAID groups, up to 256 drives (theoretical)
  • High degree of fault tolerance due to 2 parity calculations being done for each RAID 6 subset
  • Medium-to-high write transaction rate

Disadvantages

  • One of the more complex RAID implementations
  • Less space efficient than RAID 6 since separate parity calculations are done for each RAID 6 subset
  • Retrieval of parity information after a drive failure takes longer than using a mirrored solut


Depending on how you implement RAID, the benefits include one or both of the following:

Faster Performance In RAID 0, 10, 50, or 60 virtual disks, the host system can access simultaneously. This improves performance because each disk in an virtual disk has to handle of the request. For example, in a two-disk virtual disk, each disk needs to provide only its requested data.
Data Protection In RAID 1, 10, 5, 6, 50, and 60 virtual disks, the data is backed up on disk (mirror). In the RAID 5, 50, 6, or 60 virtual disks, the data is parity protected on a single multiple disks. RAID 10, 50, and 60 also allow the host to access disks simultaneously.

 

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