I have searched for data ingestion rate per day for a particular index using below search. And verified it with index size details for all servers in console of indexer cluster master under Distributed Management Console. But the total indexes size does not match between them.
index=_internal source="/opt/splunk/var/log/splunk/metrics.log" series=indexname | eval MB=kb/1024 | search group="per_index_thruput" | timechart span=1d sum(MB) by series
metrics.log will show the size of index on all indexers including the replication where as license_usage.log will show the license usage by index
use this search for license usage by index.
index=_internal source=*license_usage.log type="Usage" | eval h=if(len(h)=0 OR isnull(h),"(SQUASHED)",h) | eval s=if(len(s)=0 OR isnull(s),"(SQUASHED)",s) | eval idx=if(len(idx)=0 OR isnull(idx),"(UNKNOWN)",idx) | stats sum(b) as b by idx| eval GB=(((b/1024)/1024))/1000