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.
- 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.
- 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).