HP XP Array Manager Software - Manual (Page 12)

reduced. For this reason, the system administrator needs to maintain performance of production servers
at a high level.
Computer systems in business organizations often include development servers as well as production
servers. Development servers are used for developing, testing and debugging business applications.
If development servers suffer lowered performance, it would bring undesirable results to developers.
However, a decline in development server performance would not have as negative an impact on
the entire organization as a decline in production server performance. Therefore, production servers
should be given higher priority over development servers.
XP Performance Control allows you to limit the number of I/Os requests from development servers to
the storage system. XP Performance Control also allows you to limit the size of data to be transferred
between the development servers and the storage system. Production servers can expect reduced
response time. Production server performance can be maintained at a higher level.
Throughout this document, the term upper-limit control is used to refer to an act of limiting performance
of low-priority host servers in order to maintain high-priority host servers at a higher level.
Upper-Limit Control
Upper-limit control can help production servers to perform at higher levels, but it is not necessarily
useful when production servers are not busy.
For example, if the number of I/Os from production servers greatly increases from 9:00 a.m. to 3:00
p.m. and decreases significantly after 3:00 p.m., upper-limit control would suppress performance of
development servers even after 3:00 p.m. Development servers should be free from upper-limit control
when production servers are not busy.
XP Performance Control provides a function called threshold control. If threshold control is used,
upper-limit control is automatically disabled when traffic between production servers and the storage
system decreases to a certain level. A threshold is a value that indicates the I/O rate at which upper-limit
control is disabled. For example, if a threshold of 500 IO/s (500 I/Os per second) is applied to the
entire storage system, development servers are free from the limit on the I/O rate (that is, the number
of I/Os per second) when the number of I/Os from all the production servers is below 500 IO/s. If
the number of I/Os from the production servers increases and exceeds 500 IO/s, upper-limit control
is restored to limit the number of I/Os from the development servers again.
The threshold can be used to control the I/O rate (the number of I/Os per second) or the transfer rate
(the size of data transferred per second). For example, if a threshold of 20 MB/s (20 megabytes per
second) is set to a storage system, the I/O rate limit for development servers is disabled when the
amount of data transferred between the storage system and all the production servers is below 20
MB/s.
Interoperability with Other Products
• User types. If the user type of your user ID is storage partition administrator, you cannot use XP
Performance Control. For details on the limitations when using Performance Monitor logged in as
a storage partition administrator, see the HP StorageWorks XP24000/XP20000 Performance
Monitor User's Guide.
• I/O rates and transfer rates. XP Performance Control runs based on I/O rates and transfer rates
measured by Performance Monitor. Performance Monitor measures I/O rates and transfer rates
every second, and calculates the average I/O rate and the average transfer rate for every gath-
ering interval (specified between 1 and 15 minutes) regularly.
Suppose that 1 minute is specified as the gathering interval, and the I/O rate for the port 1-A
changes as illustrated in Graph 1 in
Figure 2 on page 13. When you use Performance Monitor
to display the I/O rate graph for 1A, the line in the graph indicates changes in the average I/O
About XP Performance Control 12