The lower-limit control is a suitable solution if you want to secure a certain level of I/O processing performance for a specific service.
CAUTION:
Set the lower-limit values for all volumes for which the LUN path is set or a namespace on the NVM subsystem with an NVM subsystem port added for NVMe is set.
Lower-limit value setting
For the initial lower-limit value, specify the minimum value in the available setting range. After you start operations, gradually increase the lower-limit value while checking the application behavior and the amount of throughput during the business cycle (for example, for one day to one week). For details about the amount of throughput, see the performance values in the QoS monitor function.
Note the following when you increase the lower-limit value:
- The sum of the lower-limit values for all volumes must be the same as or lower than the I/O processing capacity of the storage system.
- Set the lower-limit values for volumes that have a certain level of throughput. When you specify the lower-limit values for volumes on which I/Os occur intermittently, specify the minimum value in the available setting range.
- Even when you set the higher lower-limit value, if there are a few I/O requests from servers to the volume, the throughput does not increase.
When a lower-limit alert is issued
Consider the following causes when a lower-limit alert is issued or the monitor information is abnormal during operations:
- The sum of the lower-limit values for all volumes exceeds the I/O processing capacity of the storage system.
- A hardware failure (such as a drive failure) might occur. (In this case, a SIM indicating hardware failure is reported.)
In other causes, the lower-limit control might not work satisfactory. In that case, consider releasing the lower-limit setting.