Veeam Backup Space Required: Formula and Calculation
Found this really useful information in the Veeam’s forum (contributed by Anton), a great place to learn about the product and their staff are all very caring and warm.
The formulas we use for disk space estimation are the following:
Backup size = C * (F*Data + R*D*Data)
Replica size = Data + C*R*D*Data
Data = sum of processed VMs size (actually used, not provisioned)
C = average compression/dedupe ratio (depends on too many factors, compression and dedupe can be very high, but we use 50% – worst case)
F = number of full backups in retention policy (1, unless periodic fulls are enabled)
R = number of rollbacks according to retention policy (14 by default)
D = average amount of VM disk changes between cycles in percent (we use 10% right now, but will change it to 5% in v5 based on feedback… reportedly for most VMs it is just 1-2%, but active Exchange and SQL can be up to 10-20% due to transaction logs activity – so 5% seems to be good average)
