Data Availability: RAID

Selecting a RAID Level

Because of the differences in I/O performance and redundancy, one RAID level may be more appropriate than another based on the applications in the operating environment and the nature of the data being stored. When choosing a RAID level, the following performance considerations apply:

Data Availability

Availability, also known as fault-tolerance, refers to a system's ability to maintain operations and provide access to data even when one of its components has failed. In RAID volumes, availability or fault-tolerance is achieved by maintaining redundant data.

Rating the RAID Levels: Data Availability

RAID 0 RAID 1 RAID 3 RAID 5 RAID 10 RAID 0+1

None Excellent Good Good Excellent Very Good

Performance

Read and write performance can be increased or decreased depending on the RAID level you choose. Some RAID levels may be more appropriate for particular applications.

Rating the RAID Levels: Read/Write Performance

RAID 0 RAID 1 RAID 3 RAID 5 RAID 10 RAID 0+1

Reads Very Good Very Good Sequential reads: very good. Translational reads: poor. Sequential reads: good. Translational reads: very good Very Good Very Good

Writes Very Good Good Sequential writes: very good. Translational reads: poor. Fair, unless using write-back cache Fair Fair

Rebuild Performance

Rebuild performance refers to the ease with which a RAID array's data can be recovered in the event of a drive failure. RAID levels that place an emphasis on redundancy score well in this category.

Rating the RAID Levels: Rebuild Performance

RAID 0 RAID 1 RAID 3 RAID 5 RAID 10 RAID 0+1

N/A Good Fair Poor Good Good

Additional Factors

There are additional factors to consider in selecting a RAID level:

Cost Efficiency - Maintaining the redundant data or parity information associated with RAID volumes requires additional disk space. In situations where the data is temporary, easily reproduced, or non-essential, the increased cost of data redundancy may not be justified.

Mean Time Between Failure (MBTF) - Using additional disks to maintain data redundancy also increases the chance of disk failure at any given moment. Although this cannot be avoided in situations where redundant data is a requirement, it does have implications for the workload of your organization's system support staff.

Suggested Uses

Each of the RAID levels described in this section has a use for which it is ideally suited. Based on its attributes, a particular RAID level will best suit your needs.

Rating the RAID Levels: Suggested Uses

RAID 0 RAID 1 RAID 3 RAID 5 RAID 10 RAID 0+1

Non-critical data Small databases, logs, critical information Single-user data-intensive environments such as video imaging Databases and other read-intensive translational uses Data-intensive environments (large records) Medium-sized translational or data intensive uses