That is some great news! From what I read in your post, Garbage Collection feature does make a great impact on how data aging with deduplication works yet the documentation is very unclear about this
"The Garbage Collection feature optimizes the DDB performance by reducing the DDB disk IO during the data pruning process. With the Garbage Collection feature, the DDB disk is parsed once every 24 hours to mark the CommServe job records for pruning and the data aging process prunes these marked CommServe job records."
I also have to admit that event though I work with Commvault on daily basis and try to stay up-to-date I had no idea that Garbage Collection is such a huge change! Even though, from what I read, this is a default since SP14 they still even throw a warning message at you when you try to apply extended retention.
1) Is there any doc/KB/article where I can read some more about it?
Also, I just jumped into two different Commcell Environments (SP14&SP18) and I don't see the option to turn on Enable garbage collection and pruning log journaling options.
2) Do I need to run a compaction on DDB first for this option to appear?
3) And last but not least - any downsides of turning it on? Is it safe to run this on production?