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The Failover Process
Costandby State
During normal operation, shown in Figure 1, each server node in the ProLiant Cluster for
NetWare 4.2 operates as if it were a completely independent entity on the network. Server A and
Server B are allocated their own dedicated volumes on the Compaq RAID Array 4000 shared
storage. NHAS controls access for the shared storage and prevents one server from accessing the
other server’s volume. This controlling mechanism is vital to the operation of the cluster, since it
prevents a split-brain scenario, wherein two servers may try to access the same data
simultaneously; obviously, this could result in data corruption. In the given configuration, each
server is operating in the costandby state, that is, independently but waiting for the other server to
fail.
Compaq RAID Array 4000
Volume 1
Accessed by
Node A only
Volume 2
Accessed by
Node B only
Server
Node A
Server
Node B
Local Area Network
Fibre Channel Storage Hub
Data
Inter-server Monitoring
Data and Monitoring
Network Clients
Dedicated Interserver Direct Link
Fibre Channel Arbitrated Loop
NetWare
Interconnects
Server A
Volume A
Logical Connections
Server B
Volume B
Figure 1. ProLiant Cluster for NetWare 4.2 Costandby State