The amount of storage you have is a function of the size of your /var/log partition on your appliance/VM.
[Expert@Mgmt:0]# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/mapper/vg_splat-lv_current 31995824 20655304 9715228 69% /
/dev/sda1 295561 37378 242923 14% /boot
tmpfs 8151708 4 8151704 1% /dev/shm
/dev/mapper/vg_splat-lv_log 182833140 80374712 93021244 47% /var/log
Log retention period is a function of disk space, not necessarily time (though you can age log indexes based on # of days).
Logs can be rotated on either a size basis (up to 2GB) or time basis (note in R80.x this happens at midnight daily).
Both are configured here:
Logs are stored in $FWDIR/log on Management or Log server (depending on your configuration) and can be transferred to another system with standard Linux file transfer tools.
