Geographic Disk Mirroring
It is also possible to use specialized storage subsystems to geographically
mirror data across two sites. This mirroring is controlled by the
storage subsystem, and does not involve Oracle. It can be used for
disaster recovery, creating mirror sites for backup, or for creating mirrored
sites for reporting.
Geographically separated disk mirroring can be done with EMC Symmetrix
with SRDF and TimeFinder. This solution has been certified by Oracle.
This solution is good for inter-city mirroring. The solution is limited
by the bandwidth of the interconnect, and the latency associated with remote
mirroring that the application is willing to accept. In addition,
new fibre channel disk products are being offered by the hardware vendors
which can support up to 10km between mirrors. These products can
also be used to provide geographic disk mirroring solutions.
The greatest advantage of geographic disk mirroring over replication
and standby database is that these solutions have no potential for data
or transaction loss in the event of a disaster. Like synchronous
replication, these solutions wait for confirmation that the data has been
written to the mirror. However, in the event they do not receive
this confirmation within at specified period, they declare the mirror broken
and continue functioning on the primary (this behavior is configurable,
but is recommended for high availability applications).