Thank you for your hints.
I didnt find the command "storage", just "storageRM". And there are no any SAN FC events listed.
On Friday late afternoon I decided to reinstall the host back to 5.1 U1 version (all hosts were installed with HP customised ISO - 3x HP DL380p Gen8) and I disconnected FC connectivity during the installation. The result is the same as with 5.5, but if I rescan for LUNs and datastores, some of them appear for a while, but usually with wrong information about a capacity and free space. The same information is also reported on the other hosts for a few seconds or until "Refresh" is invoked.
And when I list /vmfs/volumes directory, I can see datastores name aliases, but there is some statement with datastores GUIDs:
/vmfs/volumes # ls -alix
ls: ./datastoreGUID: Function not implemented
Ondrej