I have archiving enabled in Exchange 2010 with 1 year retention for current emails. For testing, I'm setting up one user who has a total mbox size of 4 gb with Cached Mode enabled.
The result is a .ost size of 4.3 gb which in itself is okay due to Exchange's compression. However, I was hoping the size would be far less since I assumed the archive would be online and not in the .ost.
In other words:
1 year of current emails = .ost file
Older than 1 year = online archiving
Am I misunderstanding the .ost process?