Backup size increase anormally

I've recently install SP3 for Backup Exec 2010 R3 on two Windows 2008 R2 servers with Hyper-V host role (4 VM on each).

I've made a new idr for the 2 servers and then do a complete backup as recommended.

Before this installation the 2 complete backup have a size of :

- 427 Go for server 1

- 255 Go for server 2

After :

- 738 Go for server 1

- 550 Go for server 2

The jobs on the 2 servers haven't changed. No hardware change.

Any idea ?

Thanks

Christophe R.