[ Thanks to Paul
Shread for this link. ]
“Shared-disk configurations are most common in the
Fibre Channel SAN and iSCSI worlds. It is quite simple to configure
storage systems so that multiple servers can see the same logical
block device, or LUN, but without a clustered file system, chaos
will ensue if both try to use it at the same time. This problem is
dealt with by using clustered file systems, which we will cover in
a moment.“Generally speaking, shared disk setups have a single point of
failure: the storage system. This is not always true, however, as
“shared disk” is a confusing term with today’s technology. SANs,
NAS appliances and commodity hardware running Linux can all
replicate the underlying disks in real time to another storage
node, which provides a simulated shared disk environment. Since the
underlying block devices are replicated, the nodes have access to
the same data and both run a clustered file system, but this
replication breaks the traditional shared disk definition.”