The aggressiveness of Storage DRS is determined by specifying thresholds for space used and I/O latency.

Storage DRS collects resource usage information for the datastores in a datastore cluster. vCenter Server uses this information to generate recommendations for placement of virtual disks on datastores.

When you set a low aggressiveness level for a datastore cluster, Storage DRS recommends Storage vMotion migrations only when absolutely necessary, for example, if when I/O load, space utilization, or their imbalance is high. When you set a high aggressiveness level for a datastore cluster, Storage DRS recommends migrations whenever the datastore cluster can benefit from space or I/O load balancing.

In the vSphere Client, you can use the following thresholds to set the aggressiveness level for Storage DRS:

Space Utilization

Storage DRS generates recommendations or performs migrations when the percentage of space utilization on the datastore is greater than the threshold you set in the vSphere Client.

I/O Latency

Storage DRS generates recommendations or performs migrations when the 90th percentile I/O latency measured over a day for the datastore is greater than the threshold.

You can also set advanced options to further configure the aggressiveness level of Storage DRS.

Space utilization difference

This threshold ensures that there is some minimum difference between the space utilization of the source and the destination. For example, if the space used on datastore A is 82% and datastore B is 79%, the difference is 3. If the threshold is 5, Storage DRS will not make migration recommendations from datastore A to datastore B.

I/O load balancing invocation interval

After this interval, Storage DRS runs to balance I/O load.

I/O imbalance threshold

Lowering this value makes I/O load balancing less aggressive. Storage DRS computes an I/O fairness metric between 0 and 1, which 1 being the fairest distribution. I/O load balancing runs only if the computed metric is less than 1 - (I/O imbalance threshold / 100).