Databases Reference
In-Depth Information
B
Technical Comparison
of DB2 HADR with
Oracle Data Guard for
Database Disaster Recovery
O
racle Data Guard is a feature of 10g Enterprise Edition that allows for the creation
of standby databases that can be kept transactionally consistent with a primary
database. To achieve this, Oracle ships log buffers (or log files in some configurations)
from the primary server to the standby server where the log records are replayed on the
standby database. A Data Guard standby comes in two “flavors”: logical standby and
physical standby. In logical standby mode, log records are converted to SQL statements
and replayed on the standby database. This more closely resembles DB2's SQL Replica-
tion and Q Replication capabilities and as such will not be discussed here. In physical
standby mode, log records are applied using redo logic, which applies the records much
in the same fashion as would occur when rolling forward a database through log files.
In this mode, both the primary and standby databases are exact physical copies of
each other and the application of log buffers is similar to that of IBM's HADR. How-
ever, there are many differences that appear when you look just below the surface that
make HADR a superior solution to Data Guard for high-availability scenarios. A sum-
mary of the differences, each of which will be described in detail, follows.
Both IBM's HADR and Oracle's Data Guard protect from failures, such as software
failure, primary server failure, storage failure, or even primary site failure. In both cases
the configuration can include a second complete copy of the database in a remote loca-
tion to protect from any or all of these forms of failure. It should be noted that Oracle
Real Application Cluster (RAC) only protects from server and software failure on a
node in the cluster and has no protection for storage or site failure. To cover more fail-
Note:
Used with permission from Chris Eaton.
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