We've recently upgraded our Exchange from 2010 to 2016. On the 2010 servers, I was using daily reverse incrementals and once a week I would copy the latest backup, which was a full due to the nature of reverse increntals, to tape. This full backup took up 1.3TB of space both on disk and thus on tape.
We've now upgraded to Exchange 2016 and migrated all the mailboxes from the Exchange 2010 servers. On this new server, I have setup forward incremental backups. Once a week, I put a full backup to tape. However, since this is now forward incrementals, I use the synthetic full option. I am not including any rollbacks. This backup places 2TB of data on the tape.
For this new Exchange 2016 backup, I keep 2 weeks worth of forward incrementals. If I look at the repository and see how much total space is being utilized by these two weeks of incrementals, the total is 1.6TB. So how can files that total up to 1.6TB create a tape backup that is 2.0TB? And why is the synthetic full tape job for my forwrd incrementals so much larger than my tape job for the reverse incrementals?