The purge will definitively purge all the historic, the only way I see is going on the databaase side....And it is not easy, because in this historic if my memmory doesn't fails me, you have relationships at server/Sofware service level, that can be impacted.
If you go to http://CAS/DiagConsole#/sp and decrease AMD_* parameters CAS will cut the tail of data during the night.
Just first make sure how much raw/daily/monthly data you have in DMI by plying with 1period/1day/1month resolutions.
Afterwards you may of course want to restore current setting to have CAS keep i.e. 2 years of daily aggregates in the future ...
We are currently 8 months into our first year implementation.
If I understand you correctly, if I change the current 12 months value to 6, it would effectively remove the first 2 months overnight. It that correct?
No, changing AMD_MONTHLY_TRENDS_LEN property value from 12 to 6, will remove the oldest 6 months of monthly aggregates.
If you want to remove 2 oldest months you must change it from 12 to 10 it will.
So I made the change yesterday and did a test this morning by running a report on the "Last 12 months" in CAS for a Software Service. However, I still see the months of Feb and March which are the 2 oldest months that we wanted to remove. Did I need to restart the CAS?