Which bucket type contains the oldest data in the index and is read-only?

The bucket type that contains the oldest data in the index and is read-only is the cold bucket. Cold buckets are where data that is infrequently accessed is stored after it has aged out of hot and warm buckets. These buckets are optimized for storage efficiency, which allows Splunk to manage large volumes of data without consuming excessive resources.

As data transitions through the different stages or buckets in Splunk, it starts as hot, then moves to warm as it gets older and less frequently accessed. Eventually, it transitions to cold, where it is retained for longer-term storage, but cannot be actively modified. Cold data typically resides on slower, cheaper storage compared to hot or warm data, reflecting its decreased access frequency and importance.

Thus, understanding the role and characteristics of cold buckets helps in managing data lifecycle and ensuring efficient use of resources within a Splunk environment.