just to comment and avoid headaches and surprises to those who owns many 50-60 units: log into support fortinet website to read the customer bulletin that begins with:
" On October 16th, the FortiGuard Network will push out the improved IPS Engine 1.065 to all FortiOS builds. In certain rare conditions, this may cause customers on the below platforms and builds to experience loss of configuration or the rebooting of HA cluster members. This issue *only* affects customers with low-end units with 128 MB of memory and running one of the firmware versions listed below. There is no impact on customers running FortiOS 2.80. ..."
..
and ends with:
" To reduce the risk of a fault condition we strongly advise customers on older builds of FortiOS 3.00 to upgrade their devices to the most recent patched builds of MR3 or MR5 depending on which features you require:
FortiOS 3.00 MR3 Patch 9 or later (b0413-6) FortiOS 3.00 MR5 Patch 1 or later (b0564-5)"