In Zabbix, if an item's key is not unique, what is the consequence?

In Zabbix, the uniqueness of an item's key is crucial because it acts as an identifier for the data being collected from a host. If an item’s key is not unique, it means that there can be multiple items trying to record data under the same key name for the same host. As a consequence, this can lead to data being overwritten. Each new data point coming in for that key will replace the previously stored value, leading to potential loss of critical information. Therefore, administrators must ensure that each item has a unique key to avoid unintentional data loss and to maintain the integrity of monitoring.

The other options do not accurately reflect the functionality and behavior of Zabbix in this context. Creating an item does not strictly depend on uniqueness if you're operating with varied configurations or scope; thus, the inability to create the item is not a guaranteed outcome. Similarly, the value defaulting to zero is not an automatic response to non-unique keys, and the host will continue monitoring regardless of key uniqueness as long as the configuration allows for the item to exist in some form. Therefore, the focus should be on the risk of data being overwritten.