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 Server Priority Manager 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 upper-limit controls for development servers are disabled when the amount of data transferred between the storage system and the production servers is less than 20 MB per second.