The following formula estimates how much space one night's LAN backup requires, based on the number of users, their average number of messages and greetings (measured in minutes), and the system's audio encoding format.
Space used each night = 100MB + 0.05MB*(L+R) + (0.1MB*M*L*F) where:
MB represents a unit of megabytes.
L is the number of local users existing on the system that night.
R is the number of remote users existing on the system that night.
M is the average number of minutes of messages per mailbox.
F equals 1 if the system uses GSM encoding, and F equals 5 if the system uses G.711 encoding.
A G.711 system with 2,000 local users with 5 minutes of messages/greetings and 50,000 remote users would occupy approximately:
= 100MB + 0.05MB*(2000+50000) + (0.1MB*5*2000*5)
= 100 MB + 2600 MB + 5000 MB
= 7.7 GB.