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Which Is The Right Raid Level?
The answer, of course, is it depends on the application. RAID Level 3 offers
high transfer rates, and is ideal for large blocks of data where speed is of importance.
Computer Aided Design, Graphics, Scientific Computing, Image and Multimedia applications
are all good examples. RAID Level 5 arrays offer high I/O transaction rates, and are ideal
for on-line transaction processing (OLTP) applications, such as for banks, insurance
companies, hospitals, and all manner of office environments. These applications typically
perform large numbers of concurrent requests, each of which makes a small number of disk
accesses. Both RAID Levels 3 and 5 offer a good level of fault tolerance and overall
system reliability at a reasonable cost for redundancy overhead. If cost and performance
are of significantly less importance than fault tolerance and reliability, then a RAID
Level 1 solution may be an appropriate choice. Conversely, if data rate performance,
fault tolerance and reliability are not an important, then RAID Level 0 may be a suitable
choice. Transaction processing systems are usually measured by their throughput in
transactions per second (often specified as I/Os per second), rather than by the service
time for individual transactions. Many engineering and office applications consist of
programs that access large numbers of small files, such as the source files for a program
or the font libraries for a laser printer. Here is a summary of which RAID level makes the
most sense, depending upon what you are trying to do:
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Characteristics
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RAID Level(s)
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| Best Cost (best utilization of disk space) |
0, 3, & 5 |
| Best Performance (Q I/O's) |
0 & 5 |
| Best Performance (data transfer) |
3 |
| Data Availability |
1*, 3, & 5 |
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*RAID Level 1 allows high availability, but requires exactly twice the needed disk space. |
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