When you create a new Protection Group using the Create Protection Group wizard – DPM internally computes and allocates volumes for storing the replica and the shadow copies to enumerates the various formulae that we use internally to generate the default size
File system datasource
SC GBsize = (dataSourceGBSize * recoveryRangeInDays * 2) / 100 + 1 GB
Replica GBsize = (dataSourceGBSize * 3) / 2