Under Index Dashboard | Deleted index, it shows 2 partitions which are large in size.
One message partition & one attachment partition. The website says "These are partitions which have been deleted and are no longer part of any index. The underlying index files can safely be deleted".
1. Determine which Indexes are old and unused by opening the FTPartition table in the Archive Manager SQL database:
E.g.
Select * from FTPartition
2. Review the data, most likely it is the top 2 indexes (Message/Attachment) that are no longer in use. If this is the case, you can safely run the below queries:
set @partitionId1 = 1
declare @partitionId2 int
set @partitionId2 = 2
delete from FTPartition where FTPartitionID = @partitionId2
Note: Sent the partitionID accordingly. In the above two examples the queries are executed against Partition 1 and 2.