There are many ways to have shared storage. This will only cover SAN attached storage for now.
Linux servers can connect to SANs using 2 types of connectors. iSCSI and Fiber.
Fiber Easier to set up and manage
iSCSI Messier to setup but easy enough
There are also several multipathing options.
PowerPath this is an EMC product that can support various other Storage Vendors.
DM-Multipath Cheap and cheerful does the job nicely but does not have as many bells and whistles as Powerpath. Also slightly messier to setup
From Powerpath Install and manage document
Removing_luns in case you made a mess of it….. removing luns