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Performance
Considerations
There
are a number of factors that must be taken into account when calculating
the performance of any RAID or drive array system. Below are some
of the criteria that must be taken into account when calculating
the expected performance.
The
RAID Level
The RAID Level you select may offer both advantages and disadvantages
concerning performance. Some Levels offer high read cycles whilst
write cycles may drop slightly. Others offer faster write cycles
whilst the read time may increase slightly. Other levels may simply
increase performance dramatically at the expense of data protection.
For more details on this subject, see Defining
RAID Levels for an overview of industry agreed standard RAID
Levels.
The
Interface
The physical interface connecting the array members
together, and the connection between the array or RAID system and
the host can have a great impact on performance. The type of interface
used is critical to the performance. For example, a RAID array constructed
from hard disk drives ,ay be attached to each other and the host
systems by a number of different interfaces: IDE, SCSI, Ultra-Wide
SCSI, Ultra2 SCSI, Fibre-Channel, SSA, etc. each offers various
benefits and expenses. For further details, see The
Interface Decision for more information on bus widths, interface
choices, device types, and data throughput comparisons.
The
Pipeline Effect
The greater the saturation of the bus between the
members of the array and the host systems, the higher the potential
performance. However, the figures given for raw data throughput
are not the same as the data throughput you will achieve in real
life. There are many factors to take into account concerning data
throughput - and therefore expected performance. Figures quoted
for data throughput are not simply user data, but may also include
interface commands, system commands, and the general communication
between hardware. All of this reduces the potential bandwidth available
for you to read and write to the array. Please read The
Pipeline Effect for more details on this vital aspect of performance
considerations.
Related
topics:
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