Hardware
The design of GFS and of GFS2 targets SAN-like environments. Although it is possible to use them as a single node filesystem, the full feature-set requires a SAN. This can take the form of iSCSI, FibreChannel, AoE, or any other device which can be presented under Linux as a block device shared by a number of nodes, for example a DRBD device.
The DLM requires an IP based network over which to communicate. This is normally just Ethernet, but again, there are many other possible solutions. Depending upon the choice of SAN, it may be possible to combine this, but normal practice involves separate networks for the DLM and storage.
The GFS requires fencing hardware of some kind. This is a requirement of the cluster infrastructure, rather than GFS/GFS2 itself, but it is required for all multi-node clusters. The usual options include power switches and remote access controllers (e.g. DRAC, IPMI, or ILO). Fencing is used to ensure that a node which the cluster believes to be failed cannot suddenly start working again while another node is recovering the journal for the failed node. It can also optionally restart the failed node automatically once the recovery is complete.
Read more about this topic: GFS2
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