Database growth

We've had DPA running for almost 2 years now.  Currently running ver 18.2.  OS: Linux

I recently "inherited" the management of DPA (as well as the rest of our Backup/Recovery framework)

A little over a week ago, the email reports that we had been getting daily stopped.  I logged on to the server, and restarted services.  Immediately after that, my inbox got the email reports I was used to seeing.  The next day, same thing - no daily email reports.  I noticed that it was only the datastore service that had stopped.  Restarted it, and got my emails. 

Well, once, and I wouldn't worry too much, but twice in a row means something needs to be done ASAP  : )

It was then that I noticed the drive was getting full.  We had a 400gb drive which had next to no free space left.  I added 50gb, and all was well (or so I thought). I figured that should be good for a good long while.  Fast forward to today, and an additional 25gb or so has been consumed already. It's only been about a week.

After adding space, I had already gone through the Data Collection defaults - changed many things to manual (don't know if that helps much - after all, if it doesn't exist in our environment, it wouldn't take up much space anyway, right?), and reduced retention where I thought it was okay to do so without losing historical data that might one day be useful.

My questions are:

- Is this kind of growth normal? 

- Can I do something other than just reducing the data collection retention period and interval? 

- Also, why is the space taken by indexes bigger than the data itself?

Any help or insights would be appreciated