I've finally decomissioned the server, so i've get some time (and courage ;) to upgrade controller firmware to latest version (2.84) and do some test (server was off network, but with service online and with clamscan running on a loop continuously). Machine survive with wheezy kernel for a week, so seems to me that firmware upgrade (and/or wheezy kernel upgrades ;) cure the trouble. Probably the server will be trashed, anyway...