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14 Chapter 2 Overview of CCI Operations
2.2.3 Hitachi TrueCopy Takeover Commands
Figure 2.4 illustrates the server failover system configuration. When a server software error
or a node error is detected, the operation of the failover software causes the Cluster
Manager (CM) to monitor server programs, and causes the CM of the standby node to
automatically activate the HA control script of the corresponding server program. The HA
control script usually contains the database recovery procedures, server program activation
procedures, and other procedures. The takeover commands provided by Hitachi TrueCopy
are activated by the control HA script and execute the control needed for failover of the
server.
Script
Script
HORCM
(CCI)
HORCM
(CCI)
Primary/
secondary
volume
Secondary/
primary
volume
Hitachi RAID
Host A Host B
Splitting
paired
volume
Server
(Active )
Server
(standby)
CM
CM
Command device
Command device
Hitachi RAID
Swapping
Figure 2.4 Server Failover System Configuration
In a high-availability (HA) environment, a package is a group of applications that are scripted
to run on the secondary host in the event of a primary host failure. When using the HA
software (e.g., MC/ServiceGuard), the package can be transferred to the standby node as an
operation executed by the system administrator (see Figure 2.5). However, if the operation
is per
formed in an environment in which Hitachi TrueCopy is used, the volume is switched
from primary to secondary as if an error has occurred, even though data consistency is
assured. When returning the package to the current node, it is necessary to copy the
secondary volume data into the primary volume, and this operation can take as much time
as the initial copy operation for the pair. In actual operation, no package can be transferred
when TrueCopy is used. The secondary package is switched to the primary package, and vice
versa, when the primary volume is switched to the secondary volume. Therefore, the
primary and secondary TrueCopy volumes should be switched depending on the package
state.