Yes, Splunk Cloud stores data in indexers, just like an on-prem Splunk server. The biggest difference is Splunk Cloud uses SmartStore for storing warm buckets. The exact number of indexers varies for each customer and typically is not shared. You can use this query to see the indexers you have: | tstats count where index=_internal by splunk_server
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Based on which kind of cloud you have (e.g. gov / normal SC) those are going to some AWS regions. On those regions there are separate environments for every customer. Data is stored as onside to buckets on indexers. The amount of indexers is depending on your environment size (how much you are ingesting or how many SVC you have bought).