HP XP7 Storage - Manual (Page 45)

Related topics
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“Overview of Performance Control” (page 44)
Threshold control
While upper-limit control can help production servers to perform at higher levels during periods
of heavy use, it may not be desirable when production servers are not busy. For example, if the
I/O activity on production servers is high between 09:00 and 15:00 hours and decreases
significantly after 15:00, upper-limit control for development servers may not be required after
15:00.
To address this situation Performance Control provides threshold control in which upper-limit control
is automatically disabled when I/O traffic between production servers and the storage system
decreases to a user-specified level. This user-specified level at which upper-limit control is disabled
is called the threshold. You can specify the threshold as an I/O rate (number of I/Os per second)
and a data transfer rate (amount of data transferred per second).
For example, if you set a threshold of 500 I/Os per second to the storage system, the upper-limit
controls for development servers are disabled when the I/O rate of the production servers drops
below 500 I/Os per second. If the I/O rate of the production servers goes up and exceeds 500
I/Os per second, upper-limit control is restored on the development servers.
If you also set a threshold of 20 MB per second to the storage system, the data transfer rate limit
for the development servers is not reached when the amount of data transferred between the storage
system and the production servers is less than 20 MB per second.
Related topics
•
“Overview of Performance Control” (page 44)
About I/O rates and transfer rates (traffic)
Performance Control runs based on the I/O rates and data transfer rates, also called traffic,
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 sampling
interval (specified between 1 and 15 minutes) regularly. These traffic statistics reveal the number
of I/Os and amount of data being processed through the ports.
Suppose that 1 minute is specified as the sampling interval and the I/O rate at port 1-A changes
as shown in Graph 1 below. 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 rate calculated every minute
(see Graph 2). If you select the Detail check box in the Performance Monitor windows, the graph
displays changes in the maximum, average, and minimum I/O rates in one minute.
Using Performance Control you can apply upper limits and thresholds to the average I/O rate or
average transfer rate per sampling interval. For example, in the following figures, if you set an
upper limit of 150 I/Os to port 1A, the highest data point in the line CL1-A in Graph 2 and in the
line Ave. (1 min) in Graph 3 is approximately 150 I/Os. It is possible that the lines Max (1 min.)
and Min (1 min.) in Graph 3 might exceed the upper limit.
Overview of Performance Control 45