Global Network Block Device (GNBD) provides block-device access to Red Hat GFS over TCP/IP. GNBD is similar in concept to NBD; however, GNBD is GFS-specific and tuned solely for use with GFS. GNBD is useful when the need for more robust technologies — Fibre Channel or single-initiator SCSI — are not necessary or are cost-prohibitive.
GNBD consists of two major components: a GNBD client and a GNBD server. A GNBD client runs in a node with GFS and imports a block device exported by a GNBD server. A GNBD server runs in another node and exports block-level storage from its local storage (either directly attached storage or SAN storage). Refer to Figure 1.15, “GNBD Overview”
. Multiple GNBD clients can access a device exported by a GNBD server, thus making a GNBD suitable for use by a group of nodes running GFS.
Figure 1.15. GNBD Overview