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484 IBM System Storage DS6000 Series: Copy Services with IBM System z
Figure 31-10 TPC for Replication server freeze
The TPC for Replication server listens for incidents from the storage servers and takes action
when being notified of a replication error from the concerned storage server.
Figure 31-10 implies a replication error in an LSS that belongs to the session. The TPC
server receives a corresponding SNMP trap message from the concerned storage server.
The TPC for Replication server then issues a freeze command to all LSSs that are part of the
concerned session. This implies a suspend of all PPRC pairs or Copy Sets that belong to this
session. During this freeze process, write I/Os are held until the freeze process ends and the
TPC server communicates to the storage server to continue processing write I/O requests to
the concerned primary volumes in the session.
After that, write I/O can continue to the suspended primary volumes. However, both sites are
not in sync any longer but the data on the secondary site is consistent (power drop
consistent). This is a so-called freeze-and-go policy.
31.12 TPC for Replication heartbeat
Because the connectivity between the TPC for Replication server and the storage servers
that the TPC server is managing can fail, the firmware in the storage server waist for a
heartbeat signal from the TPC server. TPC for Replication can enable this heartbeat in the
corresponding LSS for Metro Mirror sessions.
Replication Manager Server
LSS
LSS
LSS
LSS
LSS
LSS
LSS
LSS
LSS
SecondariesPrimaries
Session
LSS
LSS
LSS
1
FREEZE
3
2