You have a primary database in your corporate offices, and you want to create
a standby database in another building on your local area network (LAN). In
addition, you have a legal insurance requirement to keep the redo data and
backup copies off site at a geographically distant location outside of your LAN
but on your wide area network (WAN).
You could define two destinations on your primary database so that redo data
could be transmitted to both of these sites, but this would put an
extra
workload on your primary database throughput due to the network latency of
sending the redo data over the WAN.
To solve this problem, you could define a tight connection between your
primary and physical standby databases in your LAN using the
LGWR
and
SYNC network transports and standby redo log files. This would
protect against losing access to the primary database, and it provides an
alternate site for production when maintenance is required on the primary
database. The secondary location on the WAN could be serviced by the physical
standby database, ensuring that the redo data is stored off site. Nightly
backups on the production database could then be moved to the WAN remote standby
database, which removes the requirement to ship tapes to the off-site storage
area.
Finally, in a worst case scenario, where you lose access to both the primary
database and the physical standby database on the LAN, you could fail over to
the remote standby database with minimal data loss. If you can gain access to
the redo log file of the last standby database from the original standby
database, you could recover it on the remote standby database, incurring no data
loss.
The only time you would incur problems by sending the information over the
WAN is during a switchover or failover, when the physical standby database has
transitioned to the primary role. However, this configuration would still meet
your insurance requirements.
To
reduce the load on your primary system, you can implement
cascaded destinations, whereby a standby database receives its
redo data from another standby database, instead of directly from the primary
database. You can configure a
physical standby database to retransmit the incoming redo
data it receives from the primary database to other remote destinations in the
same manner as the primary database