After upgrading to Archive Manager 4.6.x the drive where the old legacy index was located shows fluctuations in disk usage
This is expected behaviour. Until the index is fully migrated to the new format in use by Archive Manager 4.6.x onwards the old index will still be written to and read from.
This is for informational purposes only.
The behaviour described above is expected.
Run the following SQL query against the AM SQL database:
select * from FTPartition
There will be at the top of the results of the query two partitions corresponding to the 2 legacy indices (one for Messages and one for Attachments). There are two columns in the FTPartition table called 'CanRead' and 'CanWrite'. As long as the index has not fully migrated the value of this column for the legacy index partitions will be 1 (one). When this value becomes 0 (zero) then the index has fully migrated to the new type of index.