HP StorageWorks 8000 NAS - Manual (Page 28)

26 NAS 8000 Concepts
Active/Active Failover Model
In the active/active failover model, both NAS servers provide simultaneous
access to storage. Each NAS server maintains separate file systems, CIFS
shares, and NFS exports. The NAS servers do not provide shared access to
the same volumes and file systems simultaneously. Each NAS server functions
as a separate file server. To facilitate file system failover, the NAS servers
have full access to each other's disk resources but do not utilize the shared
access unless a server failure occurs. When the failure criteria have been met
and the failover system directs a NAS server to fail over, the NAS server then
takes over the IP and disk resources of the failed server and begins serving the
file systems and associated shares as if they were its own. Note that both NAS
servers provide CIFS and NFS services.
Active/Passive Failover Model
In the active/passive failover model, only one NAS server is active at a time.
The other NAS server waits in standby mode until a failover occurs. The active
NAS server operates as in the active/active model, providing both CIFS and
NFS services to client systems. Active/passive mode is created by starting
failover packages on only one primary server and configuring the secondary
server to be the failover target in the event of a primary server failure.
Resource Model
The cluster has a shared-nothing resource model, which means that each
server has exclusive access to the storage (volume groups, volumes, and
shares) and network resources (hostname, package names, IP addresses) that
it's serving. The cluster nodes can see each others’ storage and are aware of
each others' packages and IP addresses, but by agreement and design, they
activate only the storage and network addresses to which they are currently
assigned. The clustering system strictly enforces this agreement to prevent
concurrent or shared access to the same storage resources. The file system
that is used for each file volume is not distributed and does not support
simultaneous shared access. The cluster Quorum server’s primary job is to
enforce the shared-nothing cluster policy.