run zmschedulebackup as the zimbra user. without any arguments it should print your backup schedule. the default looks like this
Code:
zimbra@icarus:~> zmschedulebackup
Current Schedule:
f 0 1 * * 6 -a all
i 0 1 * * 0-5
d 1m 0 0 * * *
the last line means its set to delete backups older than 1 month. does yours have a line like this?